Name: scalable stamp printing and fabrication of hemiwicking surfaces
Uploaded: 2018-12-18T13:00:00
Description: Watch this Scientific Journal Video about Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces at JoVE.com

This material is based on research partially sponsored by the United States Office of Naval Research under Grant No. N00014-15-1-2481 and the National Science Foundation under Grant No. 1653396. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of U.S. Office of Naval Research, the National Science Foundation, or the United States Government.

1. Create the Patterning Map
<ol>
	<li>Using a graphics editor, create the desired pattern for the hemiwicking structures represented as a bitmap image. 
	NOTE: Some of the wicking design parameters (i.e., angle gradient, depth gradient) can be made to be dependent on the grayscale values assigned to each pixel. These grayscale values are then edited in order to modify the desired parameter.</li>
	<li>Save the bitmap as a portable network graphic (.png) and place the file in a readily available folder.</l...

<ol>
	<li>Plawsky, J. L., 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=Nano-+and+Micro-structures+for+Thin+Film+Evaporation+-+A+Review.">Nano- and Micro-structures for Thin Film Evaporation - A Review.</a> Nanoscale and Microscale Thermophysical Engineering. 18, 251-269 (2014).</li><li>Derjaguin, B. V., Churaev, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+question+of+determining+the+concept+of+disjoining+pressure+and+its+role+in+the+equilibrium+and+flow+of+thin+films.">On the question of determining the concept of disjoining pressure and its role in the equilibrium and flow of thin films.</a> Journal of Colloid and Interface Science. 66, 389 (1978).</li><li>Ma, H. B., Cheng, P., Borgmeyer, B., Wang, Y. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluid+flow+and+heat+transfer+in+the+evaporating+thin+film+region.">Fluid flow and heat transfer in the evaporating thin film region.</a> Microfluidics and Nanofluidics. 4 (3), 237-243 (2008).</li><li>Hohmann, C., Stephan, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscale+temperature+measurement+at+an+evaporating+liquid+meniscus.">Microscale temperature measurement at an evaporating liquid meniscus.</a> Experimental Thermal and Fluid Science. 26 (2-4), 157-162 (2002).</li><li>Potask, M., Wayner, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaporation+from+a+two-dimensional+extended+meniscus.">Evaporation from a two-dimensional extended meniscus.</a> International Journal of Heat Mass Transfer. 15 (10), 1851-1863 (1972).</li><li>Panchamgam, S. S., Plawsky, J. L., Wayner, P. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscale+heat+transfer+in+an+evaporating+moving+extended+meniscus.">Microscale heat transfer in an evaporating moving extended meniscus.</a> Experimental Thermal and Fluid Science. 30 (8), 745-754 (2006).</li><li>Arends, A. A., Germain, T. M., Owens, J. F., Putnam, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+Reflectometry+and+Interferometry+for+Measuring+Thin-film+Thickness+and+Curvature.">Simultaneous Reflectometry and Interferometry for Measuring Thin-film Thickness and Curvature.</a> Review of Scientific Instruments. 89 (5), (2018).</li><li>Zhu, Y., Antao, D. S., Lu, Z., Somasundaram, S., Zhang, T., Wang, E. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Prediction+and+characterization+of+dry+out+heat+flux+in+micropillar+wick+structures.">Prediction and characterization of dry out heat flux in micropillar wick structures.</a> Langmuir. 32 (7), 1920-1927 (2016).</li><li>Kim, J., Moon, M. W., Kim, H. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamics+of+hemiwicking.">Dynamics of hemiwicking.</a> Journal of Fluid Mechanics. 800, 57-71 (2016).</li><li>Ding, C., Soni, G., Bozorgi, P., Meinhart, C. D., MacDonald, N. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wicking+Study+of+Nanostructured+Titania+Surfaces+for+Flat+Heat+Pipes.">Wicking Study of Nanostructured Titania Surfaces for Flat Heat Pipes.</a> Nanotech Conference &amp; Expo. , (2009).</li><li>Chen, R., Lu, M. C., Srinivasan, V., Wang, Z., Cho, H. H., Majumdar, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanowires+for+Enhanced+Boiling+Heat+Transfer.">Nanowires for Enhanced Boiling Heat Transfer.</a> Nano Letters. 9 (2), 548-553 (2009).</li><li>Kim, B. S., Choi, G., Shim, D., Kim, K. M., Cho, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+roughening+for+hemi-wicking+and+its+impact+on+convective+boiling+heat+transfer.">Surface roughening for hemi-wicking and its impact on convective boiling heat transfer.</a> International Journal of Heat and Mass Transfer. 102, 1100-1107 (2016).</li><li>Mikkelsen, M. B., 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=Controlled+deposition+of+sol-gel+sensor+material+using+hemiwicking.">Controlled deposition of sol-gel sensor material using hemiwicking.</a> Journal of Micromechanics and Microengineering. 21 (11), (2011).</li><li>Haatainen, T., Ahopelto, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pattern+Transfer+using+Step&amp;Stamp+Imprint+Lithography.">Pattern Transfer using Step&amp;Stamp Imprint Lithography.</a> Physica Scripta. 67 (4), 357-360 (2003).</li><li>Chou, S. Y., Krauss, P. R., Renstrom, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoimprint+lithography.">Nanoimprint lithography.</a> Journal of vacuum Science &amp; Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena. 14 (6), 4129 (1996).</li><li>Pozzato, A., 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=Superhydrophobic+surfaces+fabricated+by+nanoprint+lithography.">Superhydrophobic surfaces fabricated by nanoprint lithography.</a> Microelectronic Engineering. 83 (4-9), 884-888 (2006).</li><li>Nair, R. P., Zou, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-nano-texturing+by+aluminum-induced+crystallization+of+amorphous+silicon.">Surface-nano-texturing by aluminum-induced crystallization of amorphous silicon.</a> Surface and Coatings Technology. 203 (5-7), 675-679 (2008).</li><li>Ashby, P. D., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultra-sensitive+Imaging+and+Interfacial+Analysis+of+Patterned+Hydrophilic+SAM+Surfaces+Using+Energy+Dissipation+Chemical+Force+Microscopy.">Ultra-sensitive Imaging and Interfacial Analysis of Patterned Hydrophilic SAM Surfaces Using Energy Dissipation Chemical Force Microscopy.</a> Journal of the American Chemical Society. 127 (18), 6814-6818 (2005).</li></ol>

A method has been introduced to create patterned pillar arrays for hemiwicking structures; this is accomplished by imprinting cavities on a plastic wafer with an engraving apparatus that follows patterning from a bitmap created by the user. A PDMS mixture is then poured, cured and coated with a thin film of aluminum via deposition. The pillar array characteristics can be customized depending on the gray scale value that is assigned in the bitmap following this protocol. This crucial aspect of patterning can crea...

Recently there has been increased interest in being able to both actively and passively control the wetting, evaporation, and mixing of fluids. Uniquely textured hemiwicking surfaces provide a novel solution for cooling techniques because these textured surfaces act as a fluid (and/or heat) pump without the moving parts. This fluid motion is driven by a cascade of capillary action events associated with the dynamic curvature of the liquid thin-film. In general, when a fluid wets a solid surface, a curved liquid thin-film (i.e., liquid meniscus) rapidly forms. The fluid thickness and curvature profile evolve until a free-energy minimum is reached. For reference, this dynamic wetting profile can rapidly decay to tens of nanometers in thickness within a spanning (fluid-wetting) length-scale of only tens of micrometers. Thus, this transitional (liquid-film) region can undergo significant changes in liquid-interface curvature. The transitional (thin-film) region is where nearly all the dynamic physics and chemistry originates. In particular, the transitional (thin-film) region is where maximum (1) evaporation rates, (2) dis-joining pressure gradients, and (3) hydrostatic pressure gradients are found1,2. As a result, curved liquid-films play a vital role in thermal transport, phase separation, fluid instabilities, and the mixing of multi-component fluids. For instance, with respect to heat transfer, the highest wall heat fluxes have been observed in this highly curved, transitional thin-film region3,4,5,6,7.
Recent hemiwicking studies have shown that the geometry (e.g., height, diameter, etc.) and placement of the pillars determine the wetting front profile and velocity of the fluid running through the structures8. As the fluid front is evaporating off the end of the last structure in an array, the fluid front is maintained at a constant distance and curvature, as the evaporated fluid is being replaced by the fluid stored in the wicking structures9. Hemiwicking structures have also been used in heat pipes and on boiling surfaces to analyze and enhance different heat transfer mechanisms.10,11,12.
One method currently used to create wicking structures is thermal imprint lithography13. This method is performed by stamping the desired layout into a resist layer on a silicon mold sample with a thermoplastic polymer stamp, then removing the stamp to maintain the microstructures. Once removed, the sample is put through a reactive ion etching process to remove any of the excess resist layer14,15. This process, however, can be sensitive to the temperature of the fabrication of the wicking structures and includes multiple steps that utilize various coatings to ensure the accuracy of the wicking structures16. It is also the case that lithography techniques are not practical for macro-scale patterning; while they still provide a way to create a pattern of microstructures on a surface, the throughput of this procedure is far less than ideal for large-scale reproduction. Considering large-scale, reproducible texturing, such as spin or dip coating, there is an inherent lack of controllable patterning. These methods create a random array of microstructures on the target surface but can be scaled to cover vastly larger areas than traditional lithography techniques17.
The protocol outlined within this report attempts to combine the strengths of traditional texturing methods while simultaneously eliminating the specific weaknesses of each; it defines a way to fabricate custom hemiwicking structures of various heights, shapes, orientations, and materials on a macro-scale and with potentially high throughput. Various wicking patterns can be quickly created for the purpose of optimization of wicking characteristics, such as directional control of fluid velocity, propagation, and mixing of different fluids. The use of different wicking structures can also provide varying thin-film thickness and curvature profiles, which can be used to systematically study the coupling between heat and mass transfer with different thickness and curvature profiles of the liquid meniscus.

<table>
	<tbody>
		<tr>
			<td>NI-DAQ 9403</td>
			<td>National Instruments</td>
			<td>370466AE-01</td>
			<td>The communication interface between the camera and the control switch for the laser.</td>
		</tr>
		<tr>
			<td>Control Switch</td>
			<td>Crouzet</td>
			<td>GN84134750</td>
			<td>A controller to use for the laser that activates the laser based on the voltage sent by the DAQ.</td>
		</tr>
		<tr>
			<td>Flea Camera</td>
			<td>FLIR</td>
			<td>FL3-U3-120S3C-C</td>
			<td>A flea camera used for imaging the drill bit on the plastic mold.&#160;</td>
		</tr>
		<tr>
			<td>Flea Imaging Camera</td>
			<td>Point Grey</td>
			<td>FL3-U3-20E4M-C</td>
			<td>A flea camera used for obtaining the side images of the pillars.</td>
		</tr>
		<tr>
			<td>200 Steps/rev, 12V-350mA Stepper Motor (x2)</td>
			<td>AdaFruit</td>
			<td>324</td>
			<td>The stepper motors are used to control the depth and angle of the end mill.&#160;</td>
		</tr>
		<tr>
			<td>10x Infinity Corrected Long Working Distance Objective</td>
			<td>Mitutoyo&#160;</td>
			<td>#46-144</td>
			<td>The objective used to get the image of the side of the pillars.</td>
		</tr>
		<tr>
			<td>15x Infinite Conjugate, UV Coated, ReflX Objective</td>
			<td>TechSpec</td>
			<td>#58-417</td>
			<td>The objective used to get the image of the top of the pillars.&#160;</td>
		</tr>
		<tr>
			<td>72002 0.002D X 0.006 LOC Carbide SQ 2FL Miniature End Mill</td>
			<td>Harvey Tools</td>
			<td>72002</td>
			<td>The drill bit that was used to create holes in the plastic mold.&#160;</td>
		</tr>
		<tr>
			<td>DC Power Delivery at 1 kW</td>
			<td>Advanced Energy</td>
			<td>MDX-1K</td>
			<td>Used to power the deposition sputterer.&#160;</td>
		</tr>
		<tr>
			<td>Turbo-V 70LP Nacro Torr Pump</td>
			<td>Varian</td>
			<td>9699336</td>
			<td>Turbo Pump used to reduce pressure inside deposition chamber.</td>
		</tr>
		<tr>
			<td>2000mw, 405nm High-Power Blue Light Focus Laser</td>
			<td>WDLasers</td>
			<td>KREE</td>
			<td>Sample Heating Laser</td>
		</tr>
		<tr>
			<td>5.875&#34; I.D. Dessicator w/ 0.25&#34; Tube Connections</td>
			<td>McMaster-Carr</td>
			<td>2204K5</td>
			<td>PDMS Dessicator</td>
		</tr>
		<tr>
			<td>SYLGARD 184 Silicone Elastomer, 0.5kg Kit</td>
			<td>Dow-Corning</td>
			<td>4019862</td>
			<td>The PDMS Kit used to make the base.</td>
		</tr>
		<tr>
			<td>Diaphragm Air Compressor / Vacuum Pump</td>
			<td>Gast</td>
			<td>DOL-701-AA</td>
			<td>Dessicator Vacuum Pump</td>
		</tr>
		<tr>
			<td>Motorized Linear Stages (2x)</td>
			<td>Standa</td>
			<td>8MT175</td>
			<td>The stepper motors used to control the sample plate in the x- and y- direction.&#160;</td>
		</tr>
		<tr>
			<td>2&#34; Diameter Unmounted Poistive Achromatic Doublets, AR Coated: 400-700 nm</td>
			<td>ThorLabs</td>
			<td>AC508-150-A</td>
			<td>The achromat was ued in order to obtain the images of the side of the pillars.&#160;</td>
		</tr>
		<tr>
			<td>Flea 3 Mono&#160; Camera, 2448 X 2048 Pixels</td>
			<td>Point Grey</td>
			<td>FL3-GE-50S5M-C</td>
			<td>A flea camera used for imiaging the top of the pillars.</td>
		</tr>
		<tr>
			<td>Digital Vacuum Transducer</td>
			<td>Thyrcont Vacuum Instruments</td>
			<td>4940-CF-212734</td>
			<td>Used for monitoring pressure inside deposition chamber.</td>
		</tr>
		<tr>
			<td>Pressurized Argon Tank Resovoir</td>
			<td>Airgas</td>
			<td>AR RP300</td>
			<td>Gas used in deposition process.</td>
		</tr>
		<tr>
			<td>1-D Translation Stage</td>
			<td>Newport Corporation</td>
			<td>TSX-1D</td>
			<td>A translation stage used to move the camera to focus on the end mill.&#160;</td>
		</tr>
		<tr>
			<td>Cylindrical Laser Mount (x2)</td>
			<td>Newport Corporation</td>
			<td>ULM-TILT-M</td>
			<td>The laser mount was used to move the camera to focus on the end mill.</td>
		</tr>
		<tr>
			<td>Benchtop Chiller with Centrifugal Pump, 120V, 60Hz</td>
			<td>Polyscience</td>
			<td>LS51MX1A110C</td>
			<td>A chiller used for the deposition assembly.</td>
		</tr>
		<tr>
			<td>Alcatel Adixen 2010SD XP, Explosion Proof Motor, Rotary Vane Vacuum Pump, 1-Phase</td>
			<td>Ideal Vacuum Products</td>
			<td>210SDMLAM-XP</td>
			<td>A vacuum pump used for the deposition assembly.&#160;</td>
		</tr>
		<tr>
			<td>Fan, 105 CFM, 115 V (x2)</td>
			<td>Comair Rotron</td>
			<td>MU2A1</td>
			<td>A fan used for cooling certain aspects of the deposition assembly.</td>
		</tr>
	</tbody>
</table>

scalable stamp printing and fabrication of hemiwicking surfaces

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. This wetting phenomenon is important in many technical fields ranging from physiology to aerospace engineering. Currently, several different techniques exist for fabricating hemiwicking structures. These conventional methods, however, are often time consuming and are difficult to scale-up for large areas or are difficult to customize for specific, nonhomogeneous patterning geometries. The presented protocol provides researchers with a simple, scalable, and cost-effective method for fabricating micro-patterned hemiwicking surfaces. The method fabricates wicking structures through the use of stamp printing, polydimethylsiloxane (PDMS) molding, and thin-film surface coatings. The protocol is demonstrated for hemiwicking with ethanol on PDMS micropillar arrays coated with a 70 nm thick aluminum thin-film.

Figure 1&#160;provides a schematic of how the stamping mechanism would create the mold for the wicking structures on a plastic mold. To investigate the quality of the stamping apparatus in manufacturing wicking films, two different pillar arrays were created to analyze the quality of the pillars for future wicking experiments. Aspects of the apparatus investigated were the accuracy of the height of the pillars (with and without a depth gradient), the quality ...

Watch this Scientific Journal Video about Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces at JoVE.com

Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces

A simple protocol is provided for the fabrication of hemiwicking structures of varying sizes, shapes, and materials. The protocol uses a combination of physical stamping, PDMS molding, and thin-film surface modifications via common materials deposition techniques.

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. ...

This method can help answer key questions in the microfluid dynamics field, such as the effects of nanostructures on a surface to the thin film profile and wicking velocity. The main advantage of this technique is that it provides a method of fabricating various wicking pillar arrays in a cost and time-efficient manner. Demonstrating the procedure will be Thomas Germain, a graduate student from our laboratory.To start, prepare the stamping device for the protocol. The essential details of this stamping device are in this schematic. A backing plate to support the mold is mounted on an XY stage.To stamp the plastic, a Theta-Z stage moves a micro sized bit. A laser heats the plastic mold at the bit tip. Here are the backing plate and the support for the stamping bit on their respective stages.A video camera fitted with a 10x objective provides a view of the stamping from a vantage to the side of the bit. Get the backing plate from the device, along with a stamping mold. The mold is an acrylic disc, one inch in diameter and one-eighth inch thick.Secure the stamping mold to the backing plate for use in the device. Next, manually translate the stamping bit out of the way to avoid damaging it. Then secure the backing plate with the mold to the motorized XY stamping stage.With the computer controls, move the plastic mold to be aligned and centered with the axis of the stamping bit. Now manually translate the stamping bit until it is almost in contact with the plastic mold. Use the computerized stamping control program and monitor the bit.Translate the stamping bit in small increments until the tip is in contact with the plastic. After that, translate the stamping bit away from the sample. Always ensure the plastic mold is normal to the bit.Or else the pillars will not have uniform height once the PDMS mold is created. Non-uniform pillar heights could affect hemiwicking of the fluid. Next, assign parameters for creating the pattern, including pixel length, cavity depth, and initial position.Continue by uploading a prepared patterning map. The grayscale value indicates the desired cavity depth, with black being the set maximum cavity depth. Start the stamping process.The software will move the bit to the proper locations using the pixel length. The bit will stamp a cavity according to the set parameters. Once the cavities have been created, remove the stamped plastic mold.Here is the stamped mold immediately after the stamping process. The mold is complete after its surface is polished with 9, 000 grit wet dry sandpaper, as with this example. Move on to use the mold to create a molding.In a beaker, put PDMS elastomer and curing agent in a 10 to 1 ratio. Then, mix them together thoroughly for three minutes. After mixing, place the beaker in an evacuated chamber to release any trapped air bubbles.Before proceeding, ensure that the mixture does not have any bubbles. Next, place the stamped plastic mold into a walled container. Ideally, the container would not be much larger than the outer diameter of the mold.Start pouring the PDMS mixture into the center of the stamped area, and spiral outward to distribute it equally. Place the container in an evacuated chamber to release air bubbles. When done, transfer the container to a hot plate to heat at 100 degrees Celsius for 15 minutes.After that, without allowing the hot plate to cool, heat it at 65 degrees Celsius for 25 minutes. Remove the container from heat and allow the PDMS to cool. Wait 20 minutes for cooling and curing before cutting the molding from the container wall.Remove the PDMS from the mold and store the plastic mold and PDMS sample in covered containers. However, before using the plastic mold, be sure to clean the surface of any residual PDMS by placing it in an ultrasound water bath for five minutes. This bitmap defines a rectangular wicking structure.Each pixel represents a square with a 100 micrometer side length. The uniformly black pixels mean each pillar in the PDMS will have the same height set to 100 micrometers. This is a top view of the pillars in the PDMS created with the bitmap.This side view from an edge demonstrates the relatively consistent height of the wicking structure. Here are side and top views of a PDMS structure with an approximately 70 micrometer thick layer of deposited aluminum. With the application of ethanol to the surface, these same structures show evidence of the fluid along the base of the pillars.Though this method can provide insight into hemiwicking dynamics, it can also be applied to other systems, such as heat pipes and nanoscale heat transfer. Following this procedure, other methods like interferometry can be performed in order to answer additional questions, like how the curvature of the meniscus is determined by the wicking structure and how that affects the heat flux in the region. After it's development, this technique paved the way for researchers in the field of microscale heat transfer to explore the role that the shape of the thin film region has on the heat blocks.Don't forget that working with lasers can be extremely hazardous, and that laser safety glasses should always be worn while the stamping process is performed.

scalable-stamp-printing-and-fabrication-of-hemiwicking-surfaces

Research

JoVE Journal

Engineering

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

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 ...

Scalable Nanohelices for Predictive Studies and Enhanced 3D Visualization

Spring-like materials are ubiquitous in nature and of interest in nanotechnology for energy harvesting, hydrogen storage, and biological sensing applications.&#160; For predictive simulations, it has become increasingly important to be able to model the structure of nanohelices accurately.&#160; To study the effect of local structure on the properties of these complex geometries one must develop realistic models.&#160; To date, software packages are rather limited in creating atomistic helical models.&#160; This work focuses on producing atomistic models of silica glass (SiO2) nanoribbons and nanosprings for molecular dynamics (MD) simulations. Using an MD model of &#8220;bulk&#8221; silica glass, two computational procedures to precisely create the shape of nanoribbons and nanosprings are presented.&#160; The first method employs the AWK programming language and open-source software to effectively carve various shapes of silica nanoribbons from the initial bulk model, using desired dimensions and parametric equations to define a helix.&#160; With this method, accurate atomistic silica nanoribbons can be generated for a range of pitch values and dimensions.&#160; The second method involves a more robust code which allows flexibility in modeling nanohelical structures.&#160; This approach utilizes a C++ code particularly written to implement pre-screening methods as well as the mathematical equations for a helix, resulting in greater precision and efficiency when creating nanospring models.&#160; Using these codes, well-defined and scalable nanoribbons and nanosprings suited for atomistic simulations can be effectively created.&#160; An added value in both open-source codes is that they can be adapted to reproduce different helical structures, independent of material.&#160; In addition, a MATLAB graphical user interface (GUI) is used to enhance learning through visualization and interaction for a general user with the atomistic helical structures.&#160; One application of these methods is the recent study of nanohelices via MD simulations for mechanical energy harvesting purposes.

Accurate modeling of nanohelical structures is important for predictive simulation studies leading to novel nanotechnology applications.&#160; Currently, software packages and codes are limited in creating atomistic helical models.&#160; We present two procedures designed to create atomistic nanohelical models for simulations, and a graphical interface to enhance research through visualization.

Spring-like materials are ubiquitous in nature and of interest in nanotechnology for energy harvesting, hydrogen storage, and biological sensing ...

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 ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

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 ...

3D Printing of Biomolecular Models for Research and Pedagogy

The construction of physical three-dimensional (3D) models of biomolecules can uniquely contribute to the study of the structure-function relationship. 3D structures are most often perceived using the two-dimensional and exclusively visual medium of the computer screen. Converting digital 3D molecular data into real objects enables information to be perceived through an expanded range of human senses, including direct stereoscopic vision, touch, and interaction. Such tangible models facilitate new insights, enable hypothesis testing, and serve as psychological or sensory anchors for conceptual information about the functions of biomolecules. Recent advances in consumer 3D printing technology enable, for the first time, the cost-effective fabrication of high-quality and scientifically accurate models of biomolecules in a variety of molecular representations. However, the optimization of the virtual model and its printing parameters is difficult and time consuming without detailed guidance. Here, we provide a guide on the digital design and physical fabrication of biomolecule models for research and pedagogy using open source or low-cost software and low-cost 3D printers that use fused filament fabrication technology.

Physical models of biomolecules can facilitate an understanding of their structure-function for the researcher, aid in communication between researchers, and serve as an educational tool in pedagogical endeavors. Here, we provide detailed guidance for the 3D printing of accurate models of biomolecules using fused filament fabrication desktop 3D printers.

The construction of physical three-dimensional (3D) models of biomolecules can uniquely contribute to the study of the structure-function relationship. 3D ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in industry. The wettability of the produced surface was analyzed by bouncing drop experiments and the topography was analyzed by confocal microscopy. In addition, we show various methodologies to measure its durability and anti-icing properties. Superhydrophobic surfaces hold a special texture that must be preserved to keep their water-repellency. To fabricate durable surfaces, we followed two strategies to incorporate a resistant texture. The first strategy is a direct incorporation of roughness to the metal substrate by acid etching. After this surface texturization, the surface energy was decreased by silanization or fluoropolymer deposition. The second strategy is the growth of a ceria layer (after surface texturization) that should enhance the surface hardness and corrosion resistance. The surface energy was decreased with a stearic acid film.
The durability of the superhydrophobic surfaces was examined by a particle impact test, mechanical wear by lateral abrasion, and UV-ozone resistance. The anti-icing properties were explored by studying the ability to repeal subcooled water, freezing delay, and ice adhesion.

We illustrate several methodologies to produce superhydrophobic metal surfaces and to explore their durability and anti-icing properties.

Several ways to produce superhydrophobic metal surfaces are presented in this work. Aluminum was chosen as the metal substrate due to its wide use in ...