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 for 4s, then at 3000rpm for 30s. </li>
 <li> Bake the wafer on a hotplate at 115&deg;C for 90s. </li>
 <li> Using the desired mask for catalyst patterning, expose the wafer to UV light with an irradiance of 20 mW/cm2 at 405 nm for 6s in hard contact mode.1.6) Bake the wafer on a hotplate again at 115&deg;C for 90s (post exposure bake). </li>
 <li> Develop the exposed photoresist for 60s using AZ-300 MIF developer. </li>
 <li> Rinse the wafer for 60s in DI water. </li>
 <li> Deposit 10nm Al2O3 followed by 1nm Fe by e-beam evaporation or sputtering. </li>
 <li> Manually scribe and break wafer into pieces approximately 20&times;20 mm or smaller. </li>
 <li> Perform lift-off of the photoresist by soaking the wafer pieces in a 1L beaker containing 100ml of acetone, while the beaker is placed in an ultrasonic bath at power 6 for 8min (CREST Ultrasonics 1100D). </li>
 <li> Dispose and replace the acetone and sonicate again with the same settings. </li>
 <li> Transfer the wafer pieces to a beaker with isopropanol (IPA), then soak for 2min. </li>
 <li> Remove the wafer pieces from the IPA individually using tweezers. Dry each piece with a gentle nitrogen stream using a handheld nozzle. </li>
</ol>
2. CNT Growth
<ol>
 <li> Acquire a bare (or oxide-coated) silicon wafer and manually scribe and break a piece with dimensions approximately 22&times;75 mm. This "boat" will be used to support and load the catalyst-coated wafer pieces into the tube furnace. The boat is very useful for holding the wafer pieces during loading and unloading, but does not play a role in the growth process. In principle the boat may be any material that is chemically and thermally stable under the CNT growth conditions. </li>
 <li> Place a desired number of catalyst-coated wafer pieces (growth substrates) on the boat, 30mm from the leading edge. </li>
 <li> Load the boat with growth substrates into the tube. Push the boat into the tube such that the leading edge is located 30mm downstream of the furnace thermocouple, using a stainless steel or quartz push rod. This 30mm position is the "sweetspot" which gives the highest CNT growth rate in our furnace. It will be necessary to determine this position for the user&#x2019;s apparatus, depending on the user&#x2019;s apparatus and objectives (e.g., maximization of CNT growth rate or density). </li>
 <li> Connect the end caps, sealing the tube. Care should be taken to not disturb the position of the boat or the patterned silicon pieces. Note: CNT growth is highly sensitive to position inside the tube. </li>
 <li> Flush the quartz tube with 1000sccm of helium for 5min at room temperature. </li>
 <li> While flowing 400sccm of hydrogen and 100sccm of helium, ramp the temperature to 775&deg;C in 10min, and then hold the flows and temperature for 10min. This step causes the film to chemically reduce from iron oxide to iron, and to dewet into nanoparticles. </li>
 <li> Change the hydrogen flow rate to 100sccm and the helium flow rate to 400sccm, while adding 100sccm of ethylene and maintaining the furnace at 775&deg;C to grow CNTs. The height of the CNTs is controlled by the duration of this step. </li>
 <li> To stop CNT growth and cool the sample, manually slide the quartz tube downstream until the catalyst chips are located approximately 1cm downstream of the furnace insulation. Use care to maintain the same flows and furnace set point temperature as in the previous step, for 15 minutes. </li>
 <li> Flush the tube with 1000sccm of helium for 5min, prior to retrieving the samples, and turning the furnace off. </li>
</ol>
3. CNT Densification
<ol>
 <li> Apply a piece of double-sided tape to an 0.8mm thick aluminum mesh with 6.25mm diameter holes. Make sure the mesh is larger than the opening of a 1L beaker and the tape is approximately centered on the mesh.</li>
 <li> Mount the silicon wafer piece with CNTs on the tape so the CNT microstructures are facing upward. </li>
 <li> Pour 100ml acetone into a 1L beaker and place the beaker on a hot plate inside a fume hood. Set the hot plate to achieve a surface temperature of 110&deg;C. Wait until the acetone starts boiling. We note that, on our hotplate, a setting of 150&deg;C was required to achieve 110&deg;C on the surface. The boiling point of acetone is much lower (approx. 56 &deg;C) but we found that the elevated temperature allowed the acetone to boil more quickly, and heated the sidewalls of the beaker, preventing condensation within the beaker. </li>
 <li> Place the aluminum mesh on the beaker such that the mounted sample is facing downwards. </li>
 <li> Note any rapid fluctuations in the vapor front rising up the side of the beaker and adjust the fume hood sash level to stabilize the vapor front. </li>
 <li> Once the vapor front approaches the top of the beaker, observe the apparent color changes on the surface of the silicon substrate. Rainbow-like patterns will appear and sweep across the entire surface. This signifies a thin film of solvent forming on the surface when the vapor comes into contact with the cold surface. </li>
 <li> Once enough solvent has been deposited, pick up the mesh and without changing the orientation of the sample, hold it away from the boiling solvent until the deposited solvent has evaporated away. The amount of time is determined empirically based on the size and spacing of the CNT structures. This is addressed further in the discussion.</li>
 <li> Remove the mesh from the beaker, and carefully peel off the sample from the double-sided tape, using a razor blade. Utmost care should be taken at this step as it is easy to break the sample during removal. </li>
</ol>
4. CNT Master Mold Fabrication
<ol>
 <li> Pool SU-8 2002 on the densified CNT microstructures. Spin the sample at 500rpm for 10s, then at 3000rpm for 30s. </li>
 <li> Bake the sample at 65&deg;C for 2 min and then at 95&deg;C for 4 min. </li>
 <li> Expose the sample to UV light with an irradiance of 75mW/cm2 for 20s. </li>
 <li> Bake the sample again at 65&deg;C for 2 min, then at 95&deg;C for 4 min. </li>
</ol>
5. Replica Molding
<ol>
 <li> If replicating delicate structures, place the master in a desiccator along with a glass vile of 100&mu;L of (tridecafluoro-1,1,2,2,-tetrahydtoocyl)-trichlorosilane at 400mTorr for 12h. </li>
 <li> Mix a total of 1g of PDMS (Sylgard 184), with a ratio of 10:1 monomer:cross-linker. For microstructures with a base size of a few micrometers and an aspect ratio of 10 or more use a ratio of 8:1. </li>
 <li> Place the CNT master in an aluminum foil dish, and pour PDMS into the dish until the sample is submerged. </li>
 <li> Place the sample in vacuum and degas at 400mTorr for 15 min. Once bubbles begin to form in the PDMS (typically after about 3 minutes) periodically increase the pressure rapidly to burst large bubbles. </li>
 <li> Cure the negative at 120&deg;C for 20 min. If the sample contains HAR structures, cure at 85&deg;C for 5h. </li>
 <li> Once cured, peel back the aluminum foil and separate the master from the soft PDMS negative by hand. </li>
 <li> If replicating delicate structures, place the negative in a desiccator along with a glass vile of 100&mu;L of (tridecafluoro-1,1,2,2,-tetrahydtoocyl)-trichlorosilane at 400mTorr for 12h. </li>
 <li> Pour SU-8 2002 into the PDMS negative and degas at 400mTorr for 10min. </li>
 <li> Bake the sample (SU-8 filled negative) at 65&deg;C for 4min, then at 95&deg;C for 6h to evaporate the solvent from the thick layer of SU-8. </li>
 <li> Expose the sample to UV light with an irradiance of 75mW/cm2 for 20s and bake again at 65&deg;C for 4min and then at 95&deg;C for 8min. </li>
 <li> Last, manually demold the SU-8 replica from the PDMS negative. </li>
</ol>
6. Representative Results
Representative as-grown CNT pillar arrays along with their densified shapes are shown in Figure 4 (image modified from De Volder et al. 4). HAR pillars with thicknesses of 10&mu;m or smaller have progressively reduced straightness, which is further reduced during densification. Densification of semicircular pillars has been shown to result in uniform bent pillars over large areas (Fig. 4c). SU-8 infiltration occurs in between and inside CNT microstructures, for structures with spacing of 30&mu;m or below a thin film of SU-8 may remain between structures. Photographs of critical steps in the replication process are shown in Figure 5, while SEM images comparing the replicated microstructures to their replicas on various scales are shown in Figure 6 (image modified from Copic et al. 5). Current limits, in terms of structure formation, including twisted structures (image modified from De Volder et al. 4), high aspect ratio walls, and re-entrant structures are shown in Figure 7 (image modified from Copic et al. 5).
<img src="/files/ftp_upload/3980/3980fig1.jpg" alt="Figure 1" /> 
Figure 1. Tube furnace setup for growth CNT growth. (a) System schematic. (b) Tube furnace (Thermo-Fisher Minimite), with cover open to show silicon boat inside sealed quartz tube. (c) Silicon boat with samples, shown before and after growth. <a href="https://www.jove.com/files/ftp_upload/3980/3980fig1large.jpg" target="_blank"> Click here to view larger figure</a>.
<img src="/files/ftp_upload/3980/3980fig2.jpg" alt="Figure 2" /> 
Figure 2. (a) Schematic of beaker setup for controlled condensation of solvent vapor onto CNT microstructures (image modified from De Volder et al. 6). (b) CNT sample substrate attached to aluminum mesh over boiling acetone.
<img src="/files/ftp_upload/3980/3980fig3.jpg" alt="Figure 3" /> 
Figure 3. Process flow for replica molding of CNT microstructures, and image of representative replicated microstructure array compared to U.S. quarter dollar coin.
<img src="/files/ftp_upload/3980/3980fig4.jpg" alt="Figure 4" /> 
Figure 4. Exemplary CNT microstructures before and after capillary forming. Schematic and SEM images of array of cylindrical CNT pillars (a) before capillary forming, and (b) after capillary forming (image modified from De Volder et al. 6). Insets show alignment and density of CNTs. (c) Semicylindrical CNT pillars densify and tilt during capillary forming, forming inclined beams (image modified from Zhao et al. 7). <a href="https://www.jove.com/files/ftp_upload/3980/3980fig4large.jpg" target="_blank"> Click here to view larger figure</a>.
<img src="/files/ftp_upload/3980/3980fig5.jpg" alt="Figure 5" /> 
Figure 5. Key steps of CNT negative mold fabrication and replica casting. (a) Casting of PDMS negative mold. (b) Degassing of the negative mold. (c) Manual demolding of the negative, and casting of the SU-8 replica.
<img src="/files/ftp_upload/3980/3980fig6.jpg" alt="Figure 6" /> 
Figure 6. Comparison of (a) CNT/SU-8 master and (b) replica micropillar structures showing high fidelity replication of micro-scale shape and nanoscale texture (i.e., sidewalls and top surface), over a large area (image modified from Copic et al. 5). <a href="https://www.jove.com/files/ftp_upload/3980/3980fig6large.jpg" target="_blank"> Click here to view larger figure</a>.
<img src="/files/ftp_upload/3980/3980fig7.jpg" alt="Figure 7" /> 
Figure 7. High-aspect-ratio (HAR) and re-entrant CNT microstructures and their polymer replicas. (a) Densified CNT honeycomb with corresponding SU8-CNT master and SU8 replica. (b) Master and replica of sloped CNT microwell (image modified from Copic et al. 5). (c) Densified twisted CNT micropillars, with master and replica of individual structure (image modified from De Volder et al. 4). The honeycombs in (a) have wall width of 400 nm and height of 20 &mu;m. <a href="https://www.jove.com/files/ftp_upload/3980/3980fig7large.jpg" target="_blank"> Click here to view larger figure</a>.

<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>

No conflicts of interest declared.

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 ...

fabrication-densification-replica-molding-3d-carbon-nanotube

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20.0K Aufrufe.  University of Michigan. Wir stellen Methoden zur Herstellung von gemusterten Mikrostrukturen von vertikal ausgerichteten Kohlenstoff-Nanoröhren (CNTs), und ihre Verwendung als Master-Formen für die Herstellung von Polymer-Mikrostrukturen mit organisierten nanoskalige Oberflächenstruktur. Die CNT-Wälder werden durch Kondensation von Lösungsmittel auf das Substrat, ein deutliches Plus an Packungsdichte und ermöglicht selbst gesteuertes Bildung von 3D-Formen verdichtet.

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

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Process of Making Three-dimensional Microstructures using Vaporization of a Sacrificial Component

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material fabrication techniques are able to mimic the complexity of these structures while maintaining scalability. The Vaporization of a Sacrificial Component (VaSC) process is able to do so. This process uses sacrificial fibers as a template to form hollow, cylindrical microchannels embedded within a matrix. Tin (II) oxalate (SnOx) is embedded within poly(lactic) acid (PLA) fibers which facilitates the use of this process. The SnOx catalyzes the depolymerization of the PLA fibers at lower temperatures. The lactic acid monomers are gaseous at these temperatures and can be removed from the embedded matrix at temperatures that do not damage the matrix. Here we show a method for aligning these fibers using micromachined plates and a tensioning device to create complex patterns of three-dimensionally arrayed microchannels. The process allows the exploration of virtually any arrangement of fiber topologies and structures.

The Vaporization of a Sacrificial Component (VaSC) process is used to fabricate microvascular structures. This procedure uses sacrificial poly(lactic) acid fibers to form hollow microchannels with precise 3D geometric positioning provided by laser micromachined guide plates.

Vascular structures in natural systems are able to provide high mass transport through high surface areas and optimized structure. Few synthetic material ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Ambient Method for the Production of an Ionically Gated Carbon Nanotube Common Cathode in Tandem Organic Solar Cells

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two solution-processed polymeric cells connected in parallel by a transparent carbon nanotubes (CNT) interlayer. This structure includes improvements in fabrication techniques for tandem OPV devices. First the need for ambient-processed cathodes is considered. The CNT anode in the tandem device is tuned via ionic gating to become a common cathode. Ionic gating employs electric double layer charging to lower the work function of the CNT electrode. Secondly, the difficulty of sequentially stacking tandem layers by solution-processing is addressed. The devices are fabricated via solution and dry-lamination in ambient conditions with parallel processing steps. The method of fabricating the individual polymeric cells, the steps needed to laminate them together with a common CNT cathode, and then provide some representative results are described. These results demonstrate ionic gating of the CNT electrode to create a common cathode and addition of current and efficiency as a result of the lamination procedure.

A method of fabricating, in ambient conditions, organic photovoltaic tandem devices in a parallel configuration is presented. These devices feature an air-processed, semi-transparent, carbon nanotube common cathode.

A method of fabricating organic photovoltaic (OPV) tandems that requires no vacuum processing is presented. These devices are comprised of two ...

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...

Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with sufficient heavy metal adsorption capacity. To this end, blast furnace slag, a residue from iron-making, is utilized as the starting material. Calcium is selectively extracted from the slag by leaching with acetic acid (2 M CH3COOH) as the extraction agent. The filtered leachate is subsequently physico-chemically purified and then carbonated to form precipitated calcium carbonate (PCC) of high purity (&lt;2 wt% non-calcium impurities, according to ICP-MS analysis). Sodium hydroxide is added to neutralize the regenerated acetate. The morphological properties of the resulting calcitic PCC are tuned for its potential application as a filler in papermaking. In parallel, the residual solids from the extraction stage are subjected to hydrothermal conversion in a caustic solution (2 M NaOH) that leads to the predominant formation of a particular zeolitic mineral phase (detected by XRD), namely analcime (NaAlSi2O6&#8729;H2O). Based on its ability to adsorb Ni2+, as reported from batch adsorption experiments and ICP-OES analysis, this product can potentially be used in wastewater treatment or for environmental remediation applications.

A protocol for the parallel production of precipitated calcium carbonate and zeolitic material from blast furnace slag via mineral carbonation and alkaline hydrothermal conversion, respectively, is presented. The performance of the zeolitic material towards nickel adsorption is tested.

The aim of this work is to present a zero-waste process for storing CO2 in a stable and benign mineral form while producing zeolitic minerals with ...

Precision Milling of Carbon Nanotube Forests Using Low Pressure Scanning Electron Microscopy

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning electron microscope (ESEM) operating with a low pressure water vapor ambient. In this technique, a portion of the electron beam interacts with the water vapor in the vicinity of the CNT sample, dissociating the water molecules into hydroxyl radicals and other species by radiolysis. The remainder of the electron beam interacts with the CNT forest sample, making it susceptible to oxidation from the chemical products of radiolysis. This technique may be used to trim a selected region of an individual CNT, or it may be used to remove hundreds of cubic microns of material by adjusting ESEM parameters. The machining resolution is similar to the imaging resolution of the ESEM itself. The technique produces only small quantities of carbon residue along the boundaries of the cutting zone, with minimal effect on the native structural morphology of the CNT forest.

Low pressure scanning electron microscopy in a water vapor ambient is used to machine nanoscale to microscale features in carbon nanotube forests.

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...