Name: fabrication, densification, and replica molding of 3d carbon nanotube microstructures
Uploaded: 2012-07-02T08:01:00
Description: Watch this Scientific Journal Video about Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures at JoVE.com

This research was supported by the Nanomanufacturing program of the National Science Foundation (CMMI-0927634). Davor Copic was supported in part by the Rackham Merit Fellowship Program at the University of Michigan. Sameh Tawfick acknowledges partial support from the Rackham Predoctoral Fellowship. Michael De Volder was supported by the Belgian Fund for Scientific Research - Flanders (FWO). Microfabrication was performed at the Lurie Nanofabrication Facility (LNF), which is a member of the National Nanotechnology Infrastructure Network; and electron microscopy was performed at the Michigan Electron Microbeam Analysis Laboratory (EMAL).

1. Catalyst Patterning
<ol>
 <li> Acquire a (100) silicon wafer with a 3000&Aring; thick silicon dioxide layer, with at least one polished side. Alternatively, you may acquire a bare silicon wafer and grow 3000&Aring; silicon dioxide on the wafer. All processing described below is done on the polished side of the wafer. </li>
 <li> Spincoat a layer of HMDS at 500rpm for 4s, then at 3000rpm for 30s. HMDS promotes adhesion between the wafer and the photoresist. </li>
 <li> Spincoat a layer of SPR-220-3 at 500rpm ...

<ol>
	<li>Xia, Y. N., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soft+lithography.">Soft lithography.</a> Annual Review of Materials Science. 28, 153-184 (1998).</li><li>Xia, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Replica+molding+using+polymeric+materials:+A+practical+step+toward+nanomanufacturing.">Replica molding using polymeric materials: A practical step toward nanomanufacturing.</a> Advanced Materials. 9, 147-149 (1997).</li><li>Tasis, D., Tagmatarchis, N., Bianco, A., Prato, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemistry+of+Carbon+Nanotubes.">Chemistry of Carbon Nanotubes.</a> Chemical Reviews. 106, 1105-1136 (2006).</li><li>De Volder, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diverse+3D+Microarchitectures+Made+by+Capillary+Forming+of+Carbon+Nanotubes.">Diverse 3D Microarchitectures Made by Capillary Forming of Carbon Nanotubes.</a> Advanced Materials. 22, 4384-4389 (2010).</li><li>Copic, D., Park, S. J., Tawfick, S., De Volder, M. F. L., Hart, A. J. <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+high-aspect-ratio+polymer+microstructures+and+hierarchical+textures+using+carbon+nanotube+composite+master+molds.">Fabrication of high-aspect-ratio polymer microstructures and hierarchical textures using carbon nanotube composite master molds.</a> Lab on a Chip. 11, 1831-1837 (2011).</li><li>De Volder, M. F. L., Park, S. J., Tawfick, S. H., Vidaud, D. O., Hart, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+and+electrical+integration+of+robust+carbon+nanotube+micropillars+by+self-directed+elastocapillary+densification.">Fabrication and electrical integration of robust carbon nanotube micropillars by self-directed elastocapillary densification.</a> Journal of Micromechanics and Microengineering. 21, 045033-04 (2011).</li><li>Zhao, Z. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bending+of+nanoscale+filament+assemblies+by+elastocapillary+densification.">Bending of nanoscale filament assemblies by elastocapillary densification.</a> Physical Review E. 82, 041605 (2010).</li><li>De Volder, M. F. L., Vidaud, D. O., Meshot, E. R., Tawfick, S., Hart, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-similar+organization+of+arrays+of+individual+carbon+nanotubes+and+carbon+nanotube+micropillars.">Self-similar organization of arrays of individual carbon nanotubes and carbon nanotube micropillars.</a> Microelectronic Engineering. 87, 1233-1238 (2010).</li><li>Nessim, G. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tuning+of+Vertically-Aligned+Carbon+Nanotube+Diameter+and+Areal+Density+through+Catalyst+Pre-Treatment.">Tuning of Vertically-Aligned Carbon Nanotube Diameter and Areal Density through Catalyst Pre-Treatment.</a> Nano Letters. 8, 3587-3593 (2008).</li><li>Pokroy, B., Epstein, A. K., Persson-Gulda, M. C. M., Aizenberg, J. <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+Bioinspired+Actuated+Nanostructures+with+Arbitrary+Geometry+and+Stiffness.">Fabrication of Bioinspired Actuated Nanostructures with Arbitrary Geometry and Stiffness.</a> Advanced Materials. 21, 463-469 (2009).</li></ol>

Lithographic patterning and preparation of the CNT catalyst substrates is straightforward and repeatable; however, achieving consistent CNT growth requires careful attention to how the height and density of CNT forests are impacted by the ambient humidity and the condition of the growth tube. In our experience, patterns larger than 1000 &mu;m2 are less sensitive to small fluctuations in the processing conditions. Further, the density of the patterns plays affects the growth density and height8. T...

<table border="1">
<tbody>
 <tr>
 <td>Name of the reagent</td>
 <td>Company</td>
 <td>Catalogue number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>4" diameter &lt;100&gt; silicon wafers coated with SiO2 (300 nm)</td>
 <td>Silicon Quest</td>
 <td>Custom</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Positive photoresist</td>
 <td>MicroChem</td>
 <td>SPR 220-3.0</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td> Hexamethyldisilizane (HMDS)</td>
 <td>MicroChem</td>
 <td>&nbsp;</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Developer</td>
 <td>AZ Electronic Materials USA Corp.</td>
 <td>AZ 300 MIF</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Sputtering system</td>
 <td>Kurt J. Lesker</td>
 <td>Lab 18</td>
 <td>Sputtering system for catalyst deposition</td>
 </tr>
 <tr>
 <td>Thermo-Fisher Minimite</td>
 <td>Fisher Scientific</td>
 <td>TF55030A</td>
 <td>Tube furnace for CNT growth</td>
 </tr>
 <tr>
 <td>Quartz tube</td>
 <td>Technical Glass Products</td>
 <td>Custom</td>
 <td>22 mm ID &times; 25 mm OD 30" length</td>
 </tr>
 <tr>
 <td>Helium gas</td>
 <td>PurityPlus</td>
 <td>He (PrePurified 300)</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>Hydrogen gas</td>
 <td>PurityPlus</td>
 <td>H2 (PrePurified 300)</td>
 <td>UHP</td>
 </tr>
 <tr>
 <td>Ethylene gas</td>
 <td>PurityPlus</td>
 <td>C2H4 (PrePurified 300)</td>
 <td>UHP</td>
 </tr>
 <tr>
 <td>Perforated aluminum sheet</td>
 <td>McMaster-Carr</td>
 <td> 9232T221</td>
 <td>For holding sample above densification beaker</td>
 </tr>
 <tr>
 <td>UV flood lamp</td>
 <td>Dymax</td>
 <td>Model 2000</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td>SU-8 2002</td>
 <td>MicroChem</td>
 <td>SU-8 2002</td>
 <td>&nbsp;</td>
 </tr>
 <tr>
 <td> Polydimethylsiloxane (PDMS)</td>
 <td>Dow Corning</td>
 <td>Sylgard 184 Silicone Elastomer Kit</td>
 <td>&nbsp;</td>
 </tr>
 </tbody>
</table>

fabrication, densification, and replica molding of 3d carbon nanotube microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

Watch this Scientific Journal Video about Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures at JoVE.com

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

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