Name: Nanomoulding di materiali funzionali, un modello versatile complementare replica Metodo di nanoimprinting (Video) | JoVE Journal
Uploaded: 2013-01-23T12:00:00.000+00:00
Duration: 10 min 49 s
Description: Impara la tecnica di nanomoulding per la patterning nanometrica a basso costo di materiali funzionali come l'ossido di zinco. Questo metodo versatile consente di produrre repliche multiple da un singolo stampo master.

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The authors thank M. Leboeuf for assistance with the AFM, W. Lee for the anodically textured aluminum master and the Swiss Federal Energy Office and the Swiss National Science Foundation for funding. A part of this work was carried out in the framework of the FP7 project "Fast Track" funded by the EC under grant agreement no 283501.

1. Mould Fabrication
We use our home-built nanoimprinting setup for the fabrication of the negative mould following Ref. 6, but any alternative nanoimprinting setup will work fine. Alternatively a functionalized polydimethylsiloxane (PDMS) mould might also work.
<ol>
 <li>Fabricate or buy a suitable master carrying the nanoscale pattern to be transferred. In principle, any master suitable for nanoimprinting will do the job. We use a textured ZnO layer on a glass sheet (Schott, AF32 eco, 41 mm x 41 mm x 0.5 mm) deposited as described in 3.1 as a master structure to illustrate the method.</li>
 <li>Apply an anti-adhesion layer on the master structure as described in 2.</li>
 <li>Clean a polyethylene naphtalate (PEN) sheet (Goodfellow, 82 mm x 41 mm x 0.125 mm) in an ultrasonic acetone bath for 2 min followed by an ultrasonic isopropanol bath for 2 more min. Rinse once more with isopropanol and blow dry with nitrogen.</li>
 <li>Deposit a sputtered Cr adhesion layer (5-10 nm) on the PEN sheet.</li>
 <li>Spin-coat the UV-curable resin (Microresist, Ormocer, 1-2 ml) on the PEN sheet at 5,000 rpm to get a uniform coverage.</li>
 <li>Perform a prebake for 5 min on a hot plate at 80 &deg;C to evaporate the solvent, improve film uniformity and adhesion to the PEN sheet.</li>
 <li>Use your nanoimprinting setup to stamp the master pattern into the UV-curable resin. Although not mandatory, we perform stamping under vacuum to prevent bubble inclusions by applying a homogenous pressure of 1 bar onto a flexible silicone membrane. In our setup, the silicone membrane separates the vacuum chamber into two sub-compartments. Pressure is generated by venting the upper compartment, while the lower compartment remains under vacuum. Venting pushes the flexible membrane towards the bottom initiating the stamping.</li>
 <li>Expose the resin to UV light to provoke the cross-linking reaction of the resin. We apply a moderate light intensity of 1.4 mW/cm2 at a wavelength of 365 nm provided by several LEDs. Exposure time through the PEN sheet is typically 15-20 min.</li>
 <li>Carefully demould by manually peeling the mould off the master structure.</li>
 <li>As the resin may undergo slight shrinkage during the deposition of the functional material, which may lead to spontaneous peeling, we perform a mild thermal post bake at 150 &deg;C during 6-8 hr in an oven with ambient atmosphere before further processing.</li>
</ol>
2. Anti-adhesion Layer
For successful demoulding, the anti-adhesion layer must be adapted to the materials and the pattern roughness. Generally rough patterns require low sticking coefficients. Low sticking coefficients on smooth patterns may lead to peeling of the functional material from the mould. High sticking coefficients on rough patterns may result in peeling of the resin from the PEN sheet during mould fabrication as the adherence of the resin to the master is stronger.
<ol>
 <li>Coat the mould (or master) with a sputtered chromium layer (5-10 nm) to promote the adhesion of the anti-adhesion agent. For smooth patterns we drop this step. In some cases the chromium layer may prevent the anti-adhesion agent to etch the master structure.</li>
 <li>Apply a small drop of anti-adhesion agent (Sigma-Aldrich, (1H, 1H, 2H, 2H-Perfluoroctyl)-trichlorsilane) on a glass slide. Put the glass slide together with the mould into a vacuum chamber and pump down. The anti-adhesion agent will evaporate and deposit as a molecular monolayer on the mould.</li>
 <li>Anchor the anti-adhesion agent via annealing during 1-2 hr at 80 &deg;C.</li>
</ol>
3. Material Deposition
We demonstrate here three deposition techniques suitable for material deposition to illustrate the versatility of nanomoulding. Other deposition techniques might also be applied. The third example describes the fabrication of a complete thin-film silicon solar cell.
<ol>
 <li>Chemical vapor deposition (CVD) of zinc oxide: Put the mould onto the heating plate of the CVD reactor heated to 180 &deg;C. Use a metal frame to avoid bending of the PEN mould during ZnO deposition. Close the reactor, pump down and allow thermalization. Admit the precursor gases (H2O and (C2H5)2Zn). In addition we dose small amounts of B2H6 for doping. The ZnO layer thickness is proportional to the deposition time. We use ZnO layer thicknesses of typically 1-5 &mu;m. Details on typical depositions parameters may be found in Ref. 7</li>
 <li>Physical vapor deposition (PVD)/sputtering of silver: Put the mould into the PVD system. Close the system and pump down. Admit argon process gas. Turn on the DC generator. The Ag layer thickness is again proportional to deposition time. We use Ag layer thicknesses of typically 1 &mu;m. Typical deposition parameters are an argon pressure of 5.5x10-3 mbar and a setup specific DC power of 250 W yielding a deposition rate of approximately 45 nm/sec.</li>
 <li>Plasma-enhanced chemical vapor deposition (PE-CVD): Deposit ZnO as in 3.1). Put the mold into the PE-CVD reactor heated to 200 &deg;C. Close the reactor, pump down and allow thermalization. Admit the precursor gases (SiH4 and H2). In addition we dose small amounts of B(CH3)3 and PH3 to achieve p- and n-type doping respectively. To increase the open-circuit voltage of the solar cells, we also use small amounts of CH4 and CO2 for the doped layers. After deposition of the p-i-n amorphous silicon solar cell stack, we deposit a ZnO backcontact as described in 3.1.</li>
 <li>Avoid excessive bending of the mould, as bending might cause peeling of the deposited layer.</li>
</ol>
4. Layer Transfer
We use glass slides (Schott AF32 eco, 41 mm x 41 mm x 0.5 mm) as final substrate. But other substrates, including metal foils or polymer sheets, could be used alternatively.
<ol>
 <li>Clean glass slides with acetone and isopropanol and blow dry with nitrogen.</li>
 <li>Spin-coat UV-curable resin (Microresist, Ormocer, 1-2 ml) on the glass slide at 5,000 rpm.</li>
 <li>Use your nanoimprinting setup to anchor the mould carrying the deposited layers onto the final substrate. As for stamping, we perform anchoring under vacuum by applying a homogenous pressure of 1 bar.</li>
 <li>Expose the resin to UV light to provoke the cross-linking reaction. We apply a moderate intensity of 1.4 mW/cm2 at a wavelength of 365 nm provided by several LEDs. Exposure time through the glass slide is only 1-3 min due to the higher UV transmission of glass compared to PEN.</li>
 <li>Demould by manually peeling the mould off the glass slide.</li>
</ol>
5. Sample Characterization
<ol>
 <li>Use your favorite morphological, electrical or optical technique to characterize the nanomoulded samples. Here we characterize our nanomoulded samples using scanning electron microscopy (SEM) and atomic force microscopy (AFM).</li>
</ol>

<ol><li>Geissler, M., Xia, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Patterning%3A+Principles+and+Some+New+Developments%5BTitle%5D)+AND+%22Advanced+Materials%22%5BJournal%5D)">Patterning: Principles and Some New Developments.</a> Advanced Materials. 16 (15), 1249-1269 (2004).</li>
<li>Guo, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanoimprint+Lithography%3A+Methods+and+Material+Requirements%5BTitle%5D)+AND+%22Advanced+Materials%22%5BJournal%5D)">Nanoimprint Lithography: Methods and Material Requirements.</a> Advanced Materials. 19, 495-513 (2007).</li>
<li>Ahn, S. H., Guo, L. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Large-Area+Roll-to-Roll+and+Roll-to-Plate+Nanoimprint+Lithography%3A+A+Step+toward+High-Throughput%5BTitle%5D)+AND+%22Application+of+Continuous+Nanoimprinting.+ACS+Nano%22%5BJournal%5D)">Large-Area Roll-to-Roll and Roll-to-Plate Nanoimprint Lithography: A Step toward High-Throughput.</a> Application of Continuous Nanoimprinting. ACS Nano. 3 (8), 2304-2310 (2009).</li>
<li>Battaglia, C., Escarré, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanoimprint+Lithography+for+High-Efficiency+Thin-Film+Silicon+Solar+Cells%5BTitle%5D)+AND+%22Nano+Letters%22%5BJournal%5D)">Nanoimprint Lithography for High-Efficiency Thin-Film Silicon Solar Cells.</a> Nano Letters. 11, 661-665 (2011).</li>
<li>Battaglia, C., Escarré, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanomoulding+of+Transparent+Zinc+Oxide+Electrodes+for+Efficient+Light+Trapping+in+Solar+Cells%5BTitle%5D)+AND+%22Nature+Photonics%22%5BJournal%5D)">Nanomoulding of Transparent Zinc Oxide Electrodes for Efficient Light Trapping in Solar Cells.</a> Nature Photonics. 5, 535-538 (2012).</li>
<li>Escarré, J., Söderström, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((High+Fidelity+Transfer+of+Nanometric+Random+Textures+by+UV+Embossing+for+Thin+Film+Solar+Cells+Applications%5BTitle%5D)+AND+%22Solar+Energy+Materials+%26+Solar+Cells%22%5BJournal%5D)">High Fidelity Transfer of Nanometric Random Textures by UV Embossing for Thin Film Solar Cells Applications.</a> Solar Energy Materials & Solar Cells. 95, 881-886 (2011).</li>
<li>Faÿ, S., Feitknecht, L., Schlüchter, R., Kroll, U., Vallat-Sauvain, E., Shah, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Rough+ZnO+layers+by+LP-CVD+process+and+their+effect+in+improving+performances+of+amorphous+and+microcrystalline+silicon+solar+cells%5BTitle%5D)+AND+%22Solar+Energy+Materials+and+Solar+Cells%22%5BJournal%5D)">Rough ZnO layers by LP-CVD process and their effect in improving performances of amorphous and microcrystalline silicon solar cells.</a> Solar Energy Materials and Solar Cells. 90, 2960-2967 (2006).</li>
<li>Zhao, X. -M., Xia, Y., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fabrication+of+Three-Dimensional+Micro-Structures%3A+Microtransfer+Molding%5BTitle%5D)+AND+%22Advanced+Materials%22%5BJournal%5D)">Fabrication of Three-Dimensional Micro-Structures: Microtransfer Molding.</a> Advanced Materials. 8, 837-840 (1996).</li>
<li>Hampton, M. J., Williams, S. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Patterning+of+Sub-500+nm+Inorganic+Oxide+Structures%5BTitle%5D)+AND+%22Advanced+Materials%22%5BJournal%5D)">The Patterning of Sub-500 nm Inorganic Oxide Structures.</a> Advanced Materials. 20, 2667-2673 (2008).</li>
<li>Bass, J. D., Schaper, C. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Transfer+Molding+of+Nanoscale+Oxides+Using+Water-Soluble+Templates%5BTitle%5D)+AND+%22ACS+Nano%22%5BJournal%5D)">Transfer Molding of Nanoscale Oxides Using Water-Soluble Templates.</a> ACS Nano. 5 (5), 4065-4072 (2011).</li>
<li>Escarré, J., Nicolay, S., et al. Nanomoulded front ZnO contacts for thin film silicon solar cell applications. Proceedings of the 27th EU-PVSEC, Frankfurt, , (2012).</li>
<li>Sontheimer, T., Rudigier-Voigt, E., Bockmeyer, M., Klimm, C., Schubert-Bischoff, P., Becker, C., Rech, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Large-area+fabrication+of+equidistant+free-standing+Si+crystals+on+nanoimprinted+glass%5BTitle%5D)+AND+%22Phys.+Status+Solidi.+RRL%22%5BJournal%5D)">Large-area fabrication of equidistant free-standing Si crystals on nanoimprinted glass.</a> Phys. Status Solidi. RRL. 5, 376-379 (2011).</li>
</ol>

No conflicts of interest declared.

Nanomoulding allows the transfer of nanopatterns on arbitrary functional materials. Comparison of the individual processing steps in Figure 1 and 2 reveals the close relationship between nanomoulding and nanoimprinting. The major difference between nanomoulding and nanoimprinting is the additional material deposition step in Figure 2e. The remaining process flow is identical. Nanomoulding can therefore be performed on any available nanoimprinting setup.
<p class="jov...

Nanopatterning has gained tremendous importance in many fields of nanotechnology and applied sciences. Pattern generation is the first step and may be accomplished by top-down approaches such as electron-beam lithography or bottom-up approaches based on self-assembly methods such as nanosphere lithography or block copolymer lithography 1. As important as pattern generation is pattern replication. Besides photolithography, nanoimprinting (Figure 1) has emerged as a promising alternative in particular suitable for high-throughput large-area nanoscale patterning at low cost 2-4. While photolithography requires a patterned mask, nanoimprinting relies on a prefabricated master structure. Pattern transfer from the master is commonly performed into a thermoplastic or a UV- or thermally curable polymer. However there are many cases, where it is desirable to transfer the pattern directly onto a functional material.
Here we describe a replication method based on nanomoulding and layer transfer (Figure 2) which we recently introduced in Ref. 5 to transfer nanoscale patterns onto functional zinc oxide electrodes. Our nanomoulding method can be easily implemented if a nanoimprinting setup is available. Nanomoulding offers the potential to be generalized to many other functional materials, materials stacks and even complete devices, provided that the mould material is chosen such that it is compatible with the material deposition process(es). As an example we present here nanomoulding of transparent conductive zinc oxide (ZnO) electrodes deposited by chemical vapor deposition (CVD) which find their application to enhance light trapping in solar cells 5.

<table><tbody><tr><td>Nanoimprinting resin</td><td>Microresist</td><td>Ormostamp</td><td></td></tr><tr><td>(1H, 1H, 2H, 2H-Perfluoroctyl)-trichlorsilane, anti-adhesion agent</td><td>Sigma Aldrich</td><td>448931-10G</td><td></td></tr><tr><td>Glass slides</td><td>Schott</td><td>AF32 eco</td><td>0.5 mm</td></tr><tr><td>Polyethylennaphtalate (PEN) sheets</td><td>Goodfellow</td><td>ES361090</td><td>0.125 mm</td></tr><tr><td>(C&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;5&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;Zn</td><td>Akzo Nobel</td><td></td><td></td></tr><tr><td>Ag sputter target 4N</td><td>Heraeus</td><td>81062165</td><td></td></tr><tr><td>B&lt;sub&gt;2&lt;/sub&gt;H&lt;sub&gt;6&lt;/sub&gt;, SiH&lt;sub&gt;4&lt;/sub&gt;, H&lt;sub&gt;2&lt;/sub&gt;, B(CH&lt;sub&gt;3&lt;/sub&gt;)&lt;sub&gt;3&lt;/sub&gt;, PH&lt;sub&gt;3&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt;, CO&lt;sub&gt;2&lt;/sub&gt;</td><td>Messer</td><td></td><td></td></tr><tr><td colspan="4">&lt;strong&gt;EQUIPMENT&lt;/strong&gt;</td></tr><tr><td>Nanoimprinting system</td><td>Home-built</td><td></td><td></td></tr><tr><td>LP-CVD system</td><td>Home-built</td><td></td><td></td></tr><tr><td>PVD system</td><td>Leybold</td><td>Univex 450 B</td><td></td></tr><tr><td>PE-CVD reactor</td><td>Indeotec</td><td>Octopus I</td><td></td></tr><tr><td>SEM</td><td>JEOL</td><td>JSM-7500 TFE</td><td></td></tr><tr><td>AFM</td><td>Digital Instruments</td><td>Nanoscope 3100</td><td></td></tr></tbody></table>

nanomoulding of functional materials, a versatile complementary pattern replication method to nanoimprinting

Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding combined with layer transfer enables the replication of arbitrary surface patterns from a master structure onto the functional material. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes. In particular we demonstrate the fabrication of patterned transparent zinc oxide electrodes for light trapping applications in solar cells.

Figure 3 summarizes some illustrative examples of nanomoulded structures. A ZnO master structure grown by CVD on glass is shown in (a). The corresponding nanomoulded ZnO replica is shown in (d). Comparison of the local height (g) and angle (j) histograms extracted from AFM images reveal the high fidelity of the nanomoulding process. Analogous results are shown for a one-dimensional grating fabricated by interference lithography (b,e,h,k) and anodically textured aluminum (c,f,i,l).
<p class="jo...

We describe a nanomoulding technique which allows low-cost nanoscale patterning of functional materials, materials stacks and full devices. Nanomoulding can be performed on any nanoimprinting setup and can be applied to a wide range of materials and deposition processes.

We describe a nanomoulding technique which  allows low-cost nanoscale patterning of functional materials, materials stacks  and full devices. Nanomoulding ...

The overall aim of this procedure is to transfer a pattern from an arbitrary master structure to a functional material. This video illustrates the procedure using zinc oxide as a functional material pattern transfer is accomplished by first fabricating a negative mold from the master structure. The second step is to create the zinc oxide replica by first adding an antis stick layer onto the mold, followed by zinc oxide deposition, the zinc oxide is then anchored to the final glass substrate using a UV cured resin and finally released from its mold.Ultimately, multiple functional replicas can be prepared from a single master mold using this technique While another printing serves traditionally to pattern a UV or thermally curable resin. Nano molding offers the potential to be generalized to many other functional materials, material stacks, and even complete devices, provided that the mold material is chosen compatible with the material deposition process. We first had the idea for this method when we tried to find a way to obtain a transparent conductive nano imprinted electrode as commercially available Nano printing resins are insulating.We had to find another way and that's why w

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Impara la tecnica di nanomoulding per la patterning nanometrica a basso costo di materiali funzionali come l'ossido di zinco. Questo metodo versatile consente di produrre repliche multiple da un singolo stampo master.

Nanomoulding of Functional Materials, a Versatile Complementary Pattern Replication Method to Nanoimprinting

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