Name: glass-based devices to generate drops and emulsions
Uploaded: 2022-04-05T13:00:00
Description: Watch this Scientific Journal Video about Glass-Based Devices to Generate Drops and Emulsions at JoVE.com

We are thankful to the ACS PRF (grant 60302-UR9), Agrobio S.L. (contract #311325), and MCIN/AEI/10.13039/501100011033/FEDER, UE (grant No. PID2021-122369NB-I00).

1. Making simple drops
<ol>
	<li>For making simple drops, use a glass base made with a microscope slide (76.2 mm x 25.4 mm) to build the device. This allows for easy transportation and visualization of the liquids through the glass.</li>
	<li>Use a round glass capillary for the tip. For this protocol, use 1 mm diameter round capillaries (readily available in a wide range of sizes).
	<ol>
		<li>To make a tip with the desired diameter, pull the capillary using a micropipette pulling machine until two hal...

<ol>
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R., Fernandez-Nieves, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drop+size+control+in+electro-coflow.">Drop size control in electro-coflow.</a> Applied Physics Letters. 99 (2), 021910 (2011).</li><li>Cloupeau, M., Prunet-Foch, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrostatic+spraying+of+liquids:+Main+functioning+modes.">Electrostatic spraying of liquids: Main functioning modes.</a> Journal of Electrostatics. 25 (2), 165-184 (1990).</li><li>Jaworek, A., Krupa, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Main+modes+of+electrohydrodynamic+spraying+of+liquids.">Main modes of electrohydrodynamic spraying of liquids.</a> Third International Conference on Multiphase Flow ICMF. , (1998).</li><li>Juraschek, R., R&#246;llgen, F. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pulsation+phenomena+during+electrospray+ionization.">Pulsation phenomena during electrospray ionization.</a> International Journal of Mass Spectrometry. 177 (1), 1-15 (1998).</li><li>Guerrero, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Emission+modes+in+electro+co-flow.">Emission modes in electro co-flow.</a> Physics of Fluids. 31 (8), 082009 (2019).</li><li>Utada, A. S., Fern&#225;ndez-Nieves, A., Stone, H. A., Weitz, D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dripping+to+jetting+transitions+in+coflowing+liquid+streams.">Dripping to jetting transitions in coflowing liquid streams.</a> Physical Review Letters. 99 (9), 094502 (2007).</li><li>Castro-Hern&#225;ndez, E., Gundabala, V., Fern&#225;ndez-Nieves, A., Gordillo, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Scaling+the+drop+size+in+coflow+experiments.">Scaling the drop size in coflow experiments.</a> New Journal of Physics. 11, 075021 (2009).</li><li>Godfray, H. C. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Food+Security:+the+challenge+of+feeding+9+billion+people.">Food Security: the challenge of feeding 9 billion people.</a> Science. 327 (5967), 812-818 (2010).</li><li>Labb&#233;, R., Gagnier, D., Kostic, A., Shipp, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+function+of+supplemental+foods+for+improved+crop+establishment+of+generalist+predators+Orius+insidiosus+and+Dicyphus+hesperus.">The function of supplemental foods for improved crop establishment of generalist predators Orius insidiosus and Dicyphus hesperus.</a> Scientific Reports. 8 (1), 17790 (2018).</li><li>Pilkington, L. J., Messelink, G., van Lenteren, J. C., Le Mottee, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=34;Protected+Biological+Control&amp;#34;+-+Biological+pest+management+in+the+greenhouse+industry.">34;Protected Biological Control&amp;#34; - Biological pest management in the greenhouse industry.</a> Biological Control. 52 (3), 216-220 (2010).</li><li>Benson, C. M., Labbe, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploring+the+Role+of+Supplemental+Foods+for+Improved+Greenhouse+Biological+Control.">Exploring the Role of Supplemental Foods for Improved Greenhouse Biological Control.</a> Annals of the Entomological Society of America. 114 (3), 302-321 (2021).</li><li>Temiz, U., &#214;zt&#252;rk, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Encapsulation+methods+and+use+in+animal+nutrition.">Encapsulation methods and use in animal nutrition.</a> Selcuk Journal of Agricultural and Food Sciences. 32 (3), 624-631 (2018).</li><li>Messelink, G. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Approaches+to+conserving+natural+enemy+populations+in+greenhouse+crops:+current+methods+and+future+prospects.">Approaches to conserving natural enemy populations in greenhouse crops: current methods and future prospects.</a> BioControl. 59, 377-393 (2014).</li><li>Mu&#241;oz-C&#225;rdenas, K., 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=Generalist+red+velvet+mite+predator+(Balaustium+sp.)+performs+better+on+a+mixed+diet.">Generalist red velvet mite predator (Balaustium sp.) performs better on a mixed diet.</a> Experimental &amp; Applied Acarology. 62 (1), 19-32 (2014).</li><li>van Lenteren, J. C., Bolckmans, K., K&#246;hl, J., Ravensberg, W. J., Urbaneja, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+control+using+invertebrates+and+microorganisms:+plenty+of+new+opportunities.">Biological control using invertebrates and microorganisms: plenty of new opportunities.</a> BioControl. 63, 39-59 (2018).</li><li>Urbaneja-Bernat, P., Alonso, M., Tena, A., Bolckmans, K., Urbaneja, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sugar+as+nutritional+supplement+for+the+zoophytophagous+predator+Nesidiocoris+tenuis.">Sugar as nutritional supplement for the zoophytophagous predator Nesidiocoris tenuis.</a> BioControl. 58 (1), 57-64 (2013).</li><li>Vila, E., Cabello, T., Guevara-Gonzalez, R., Torres-Pacheco, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biosystems+Engineering+Applied+to+Greenhouse+Pest+Control.">Biosystems Engineering Applied to Greenhouse Pest Control.</a> Biosystems Engineering: Biofactories for Food Production in the Century XXI. , (2014).</li><li>Riudavets, J., Moerman, E., Vila, E., LodovicaGullino, M., Albajes, R. 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The protocol to fabricate three different glass-based devices has been described above. In the case of the device to generate simple drops, the flow rate and liquid properties are crucial to generate drops in a controlled manner. Drops will form at the tip in the dripping regime, or at the end of the jet in the jetting regime. The transition from dripping to jetting is parametrized by the dimensionless Weber number, We23. This number represents the ratio between inertial and surface tension forces...

Controlled generation of drops in the micron and nanoscale with a narrow size distribution is a challenging task. These drops are of interest for the engineering of soft materials with many applications in science and technology1,2,3,4,5,6.
The most common devices for the high production rate&#160;of drops are mixers7 and ultrasound emulsificators8. These methods are simple and low cost, but they typically result in polydisperse drops with a wide range of sizes. Hence, additional steps are required to produce monodisperse samples. Microfluidic devices can be designed differently to provide an efficient way to drop formation. Additionally, the usually low flow rates involved (i.e., low Reynolds number) allow for great&#160;control over the fluid flow.
While microfluidic devices are commonly made using lithographic techniques with poly(dimethyl) siloxane (PDMS), this manuscript focuses on glass-based capillary devices. PDMS devices are usually chosen for their ability to design complex channel patterns and because of their scalability. Glass devices, on the contrary, are rigid and have greater solvent resistance than their PDMS counterparts. Additionally, glass can be modified to change its wettability, which allows controlling the generation of complex emulsions. Being able to independently treat the nozzle and channel walls enables the formation of drops in a controlled and reproducible manner, while assuring&#160;the stability of the resultant emulsions if the drops were to touch the walls9; otherwise the drops may coalesce and accumulate at the wall. Another difference between these two types of devices is that in glass-based devices, the flow is three-dimensional, while it is planar in conventional PDMS devices. This fact minimizes the drop contact with the channel walls so that the influence of contact lines can be neglected10, thereby protecting the stability of multiple emulsion drops.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/63376/63376fig01.jpg" /> 
Figure 1: Different microfluidic device configurations. Sketches of (A) a T-junction, (B) a coflowing device, and (C) a flow-focusing device. <a href="https://www.jove.com/files/ftp_upload/63376/63376fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
There are three main geometries used, namely T-junction11, flow focusing12,13, and coflow14. In the T-junction geometry, the dispersed phase contained in the channel perpendicularly intersects the main channel which houses the continuous phase. The shear stress exerted by the continuous phase breaks the incoming dispersed liquid resulting in drops. The generated drops are limited in lower size by the dimensions of the main channel11. In the flow-focusing geometry, the two fluids are forced through a small orifice that is located in front of the injection tube. The result is&#160;the formation of a jet, which is much smaller than the injection tube12,13. Finally, the coflow geometry has a configuration characterized by the coaxial flow of two immiscible fluids14. In general, dripping and jetting can be observed depending on the operating conditions. The dripping regime occurs at low flow rates and the resulting droplets are very monodisperse and have a diameter proportional to the tip size. The drawback is its low production frequency. The jetting regime occurs at higher flow rates as compared to the dripping regime. In this case, the drop diameter is directly proportional to the diameter of the jet which can be much smaller than the diameter of the tip under the right conditions.
An alternative to these hydrodynamic approaches relies on the additional use of electric forces. Electrospray is a well-known and widely used technique for generating droplets. It is based on the principle that a liquid with a finite electrical conductivity will deform in the presence of a strong electric field. The liquid will eventually adopt a conical shape resulting from&#160;the balance between electric and surface tension stresses15. The process starts with the electric field inducing an electric current in the liquid that causes charges to accumulate at the surface. The presence of the electric field results in an electric force on these charges, which drags the liquid along, elongating the meniscus in the direction of the field. Under different conditions, the meniscus can either shed the charged drops or may emit one or several jets which then break into drops15. Although these electrically assisted microfluidic methods naturally allow the generation of small drops, they suffer from a lack of a steady-state operation that compromises the emulsion monodispersity. The resultant charged drops tend to discharge on the confining walls and/or anywhere in the device where the electric potential is lower than the imposed external voltage. Thus, the electrified meniscus becomes unstable, ultimately emitting drops in a chaotic way and causing their uncontrolled production and loss of monodispersity.
In electro-coflow, the electrical and hydrodynamic stresses are coupled in a coflow microfluidic device16 similar to the one used for generating double emulsions12. Two main features allow electro-coflow to be successful in reaching a steady-state emission regime: (i) the dispersed phase is ejected into another coflowing viscous liquid, and (ii) the use of a liquid counter-electrode or ground. Having a flowing outer liquid has proven to change the geometric properties of the drop emission process17. The liquid counter-electrode allows the discharge and extraction of the resultant drops, assuring the steady-state generation of drops. In addition, by exploiting the balance of electrical and hydrodynamic forces, the resultant drop sizes can potentially vary within a&#160;wider range than the sizes that can be covered by any of the previously mentioned techniques.
This detailed video protocol is intended to help new practitioners in the&#160;use and fabrication of glass-based microfluidics.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-[methoxy(polyethyleneoxy)6-9propyl] trimethoxysilane.</td>
			<td>Gelest</td>
			<td>SIM6492.7</td>
			<td></td>
		</tr>
		<tr>
			<td>Ceramic tile</td>
			<td>Sutter</td>
			<td>CTS</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylene glycol</td>
			<td>Fisher</td>
			<td>BP230</td>
			<td>These can be found at other companies like Sigma-Aldrich</td>
		</tr>
		<tr>
			<td>Hexane</td>
			<td>Sigma- Aldrich</td>
			<td>34859</td>
			<td>Available in other vendors</td>
		</tr>
		<tr>
			<td>ITW Polymers Adhesives Devcon 5 Minute Epoxy Adhesive 25 mL Dev-Tube</td>
			<td>Ellsworth adhesives</td>
			<td>470740</td>
			<td></td>
		</tr>
		<tr>
			<td>Microforge</td>
			<td>Narishige</td>
			<td>MF 830</td>
			<td></td>
		</tr>
		<tr>
			<td>Micropipette puller</td>
			<td>Sutter</td>
			<td>P97</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope slides</td>
			<td>Fisher</td>
			<td>12-544-1</td>
			<td>Available in other vendors</td>
		</tr>
		<tr>
			<td>Needle 20 Gauge, .0255&#34; ID, .0355&#34; OD, 1/2&#34; Long</td>
			<td>McMaster</td>
			<td>75165A677</td>
			<td></td>
		</tr>
		<tr>
			<td>SDS</td>
			<td>Sigma-aldrich</td>
			<td>428015</td>
			<td>Surfactant</td>
		</tr>
		<tr>
			<td>Silicone oil</td>
			<td>Clearco</td>
			<td>PSF-10cSt</td>
			<td>The catalog number correspond to the 10cSt viscosity oil. Different viscosity oils can be found at this company</td>
		</tr>
		<tr>
			<td>Span 80</td>
			<td>Fisher</td>
			<td>S0060500G</td>
			<td>non-ionic surfactant</td>
		</tr>
		<tr>
			<td>Square glass capillary 2mm ID (borosillicate 300 or 600 mm long)</td>
			<td>VitroCom</td>
			<td>S 102</td>
			<td></td>
		</tr>
		<tr>
			<td>Standard Glass Capillaries, 6 in., 2 / 1.12 OD/ID</td>
			<td>World Precision instruments</td>
			<td>1B200-6</td>
			<td>These can be found at other companies like Sutter or Vitrocom</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>Chemyx</td>
			<td>FUSION 100-X</td>
			<td>This model has a good quality/price ratio</td>
		</tr>
		<tr>
			<td>Syringes (it will depend on the compatibility with the liquids)</td>
			<td>Fisher</td>
			<td></td>
			<td>Catalog number will depend on the size</td>
		</tr>
		<tr>
			<td>Trimethoxy(octyl)silane</td>
			<td>Sigma- Aldrich</td>
			<td>376221</td>
			<td>Available in other vendors</td>
		</tr>
		<tr>
			<td>Tubing ( it will depend on the compatibility with the liquids)</td>
			<td>Scientific commodities</td>
			<td>BB3165-PE/5</td>
			<td>This reference is for polyethylene micro tubing. The size fits the needle size listed here</td>
		</tr>
	</tbody>
</table>

glass-based devices to generate drops and emulsions

In this manuscript, three different step-by-step protocols to generate highly monodisperse emulsion drops using glass-based microfluidics are described. The first device is built for the generation of simple drops driven by gravity. The second device is designed to generate emulsion drops in a coflowing scheme. The third device is an extension of the coflowing device with the addition of a third liquid that acts as an electric ground, allowing the formation of electrified drops that subsequently discharge. In this setup, two of the three liquids have an appreciable electrical conductivity. The third liquid mediates between these two and is a dielectric. A&#160;voltage difference applied between the two conducting liquids creates an electric field that couples with hydrodynamic stresses of the coflowing liquids, affecting the jet and drop formation process. The addition of the electric field provides a path to generate smaller drops than in simple coflow devices and for generating particles and fibers with a wide range of sizes.

In this manuscript, three different devices have been designed to generate drops. We have generated drops with a size of (3.29 &#177; 0.08) mm&#160;(Figure 4B) and (1.75 &#177; 0.04) mm&#160;(Figure 4C) using the device described in step 1. The emulsion drops can be generated using the coflow and the electro-coflow devices. For the latter, we show dripping in Figure 9, while cone-jet and whipping modes are shown in <strong class="xf...

Watch this Scientific Journal Video about Glass-Based Devices to Generate Drops and Emulsions at JoVE.com

Glass-Based Devices to Generate Drops and Emulsions

Here, a protocol to manufacture glass-based microfluidic devices used for generating highly monodisperse emulsions with controlled drop size is presented.

In this manuscript, three different step-by-step protocols to generate highly monodisperse emulsion drops using glass-based microfluidics are described. ...

This protocol describes how to fabricate glass based microfluidic devices in detail. Following this protocol will allow anyone without experience to build and use these devices. With glass, we can easily render surfaces hydrophobic or hydrophilic thus making glass based devices attractive for generating stable emulsion drops.There are multiple applications for drops and emulsions in fields as diverse as cosmetic, the food industry, and drug delivery. In this manuscript, we emphasize a bit more on their use in intensive agriculture. We recommend being patient at each step.Also check that the tip is clean and not broken. Do not wait until the device is completed to check these. For making simple drops, use a glass base made with a microscope slide to build the device.For the tip, use one millimeter diameter round glass capillaries. Next, use a 20 gauge syringe needle to facilitate introducing the liquid into the capillary. Using a razor blade or a scalpel, carve a hole equal to the size of the outer diameter of the capillary at the base of the needle.Rinse the needle with water to remove any dust and fibers from cutting and allow the needle to air dry. To assemble the device, glue the round capillary to the microscope slide by placing the tip of the capillary one to two centimeters outside the end of the microscope slide and adding a dab of epoxy at the center of the capillary such that it will not interfere with the field of vision or with the syringe needle. Next, place the syringe needle such that the end of the capillary sits at the center of the needle and put a small amount of hardened epoxy around the rim at the bottom of the needle.After a few minutes, apply the second layer of fresh epoxy, covering the base of the needle and avoiding the hole. Then, cover the hole with hardened epoxy to prevent the epoxy from flowing inside the needles. For generating drops, place the device in a vertical position using a clamp such that the tip is facing down like a kitchen faucet.Use a syringe pump or a pressure driven setup to pump the liquid into the device. For making emulsion drops, use a five centimeter long square capillary for the outer liquid and a one millimeter diameter round capillary. Ensure that the length of the round capillary is several centimeters longer than the square capillary.Match the outer diameter of the round capillary to the inner size of the square capillary to ensure that both capillaries are coaxially aligned. Next, to assemble the device, glue the square capillary to the microscope slide by placing the tip of the capillary one to two centimeters outside the end of the microscope slide and applying a dab of epoxy at the center of the capillary. Wait until the epoxy cures completely.Then, introduce the round capillary into the square capillary such that the end of the round capillary on the slide is a few centimeters from the end of the square capillary. The other end of the round capillary which is inside the square capillary should be at a distance approximately equal to the diameter of the round capillary from the end of the square capillary. Glue the round capillary using a dab of epoxy at mid-distance between the end of the round capillary and the beginning of the square capillary and wait until the epoxy cures completely.To house the capillary in the needle base, carve a hole at the base of the round cap which is the size of the outer diameter of the capillary. Then, to fit the other needle at the end of the square capillary, carve a round and a square hole at the base of the needle to accommodate the joint. After cutting, rinse the needles with water and let them air dry.Then glue them as demonstrated earlier. To build the microfluidic device, cut two small pieces of a slide and using epoxy, glue them to two microscope slides to keep the slides together. Wait until the epoxy cures completely.Using a diamond scribe, cut the square capillary to a length of approximately four centimeters. Use the square capillary with an inner side that matches the outer diameter of the round capillary to align the capillaries coaxially. For this protocol, use a two millimeter side capillary.Then, using a pipette pulling machine, pull a round capillary to obtain two half capillaries with a thin tip. Next, using a micro forge, cut the tip of one of the half capillaries to the desired diameter. To use the other half as a collector capillary, cut the pulled tip so that the original flat ends are recovered.Glue the square capillary to the slides. Do not put the capillary in the middle of the slides as the joints of the slides should not be in the viewing region. Then, place the tip and collector capillary inside the square capillary around two millimeters apart.To avoid the joint, place the ends of both the tip and collector capillaries on the same side. To fabricate connections to the open ends of the capillaries, place four needles covering these ends and glue the needles as demonstrated earlier. To test the device for leaks, close two of the needles using a bent piece of tubing held by a binder clip.Then, using a syringe, manually pump deionized water into the device through one of the needles using the last needle as an exit. If no leakages are observed, pump the water through the next needle repeating the process for all four needles. If a leak is found, thoroughly dry the device, apply epoxy, and wait for one hour before testing again.After confirming no leakage, fill the device with experimental liquid and remove air bubbles. Then connect the inner liquid or dispersed phase syringe to needle one, the outer liquid or continuous phase to needle two, and the collector liquid or counter electrode to needle four. Needle three is for the exit.Finally, connect the power supply to the needles feeding the inner and collector liquids to set a potential difference between the tip and collector liquid. In this study, approximately 3.3 millimeter silicone oil drops were generated using a 580 micrometer tip. And 1.75 millimeter drops were generated using an 86 micrometer tip.Additionally, emulsion drops were generated using electro co flow devices in the dripping, cone jet, and whipping modes. In these results, the same liquid is used as inner and collector liquids. However, if the experiments goal is collecting these drops, a different conducting liquid should be used as a collector.Be patient and wait until the epoxy cures. If it gets wet, it will never dry and you will need to start the entire procedure again. Multiple emulsions can be generated using in combinations of flow focus in a scheming series.Each extra scheme will add a shell to the motion drop. Flow focusing sections can also be used.

glass-based-devices-to-generate-drops-and-emulsions

Research

JoVE Journal

Engineering

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

Picoinjection of Microfluidic Drops Without Metal Electrodes

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of these electrodes adds cumbersome and error-prone steps to the device fabrication process. We have developed a technique that obviates the needs for metal electrodes during picoinjection. Instead, it uses the injection fluid itself as an electrode, since most biological reagents contain dissolved electrolytes and are conductive. By eliminating the electrodes, we reduce device fabrication time and complexity, and make the devices more robust. In addition, with our approach, the injection volume depends on the voltage applied to the picoinjection solution; this allows us to rapidly adjust the volume injected by modulating the applied voltage. We demonstrate that our technique is compatible with reagents incorporating common biological compounds, including buffers, enzymes, and nucleic acids.

We have developed a technique for picoinjecting microfluidic drops that does not require metal electrodes. As such, devices incorporating our technique are simpler to fabricate and to use.

Existing methods for picoinjecting reagents into microfluidic drops require metal electrodes integrated into the microfluidic chip. The integration of ...

In Situ Time-dependent Dielectric Breakdown in the Transmission Electron Microscope: A Possibility to Understand the Failure Mechanism in Microelectronic Devices

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. The aggressive scaling of feature sizes, both on devices and interconnects, leads to serious challenges to ensure the required product reliability. Standard reliability tests and post-mortem failure analysis provide only limited information about the physics of failure mechanisms and degradation kinetics. Therefore it is necessary to develop new experimental approaches and procedures to study the TDDB failure mechanisms and degradation kinetics in particular. In this paper, an in situ experimental methodology in the transmission electron microscope (TEM) is demonstrated to investigate the TDDB degradation and failure mechanisms in Cu/ULK interconnect stacks. High quality imaging and chemical analysis are used to study the kinetic process. The in situ electrical test is integrated into the TEM to provide an elevated electrical field to the dielectrics. Electron tomography is utilized to characterize the directed Cu diffusion in the insulating dielectrics. This experimental procedure opens a possibility to study the failure mechanism in interconnect stacks of microelectronic products, and it could also be extended to other structures in active devices.

In Situ Time-dependent Dielectric Breakdown in the Transmission Electron Microscope: A Possibility to Understand the Failure Mechanism in Microelectronic Devices

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. This paper demonstrates the procedure of an in situ TDDB experiment in the transmission electron microscope, which opens a possibility to study the failure mechanism in microelectronic products.

The time-dependent dielectric breakdown (TDDB) in on-chip interconnect stacks is one of the most critical failure mechanisms for microelectronic devices. ...

Thermal Measurement Techniques in Analytical Microfluidic Devices

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. Micromachining techniques allow reduction of the thermal mass of fabricated structures and introduce the possibility to perform high sensitivity thermal measurements in the micro-scale and nano-scale devices. Combining thermal measurement techniques with microfluidic devices allows performing different analytical measurements with low sample consumption and reduced measurement time by integrating the miniaturized system on a single chip. The procedures of thermal measurement techniques for particle detection, material characterization, and chemical detection are introduced in this paper.

Here, we present three protocols for thermal measurements in microfluidic devices.

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Preparation and 3D Tracking of Catalytic Swimming Devices

We report a method to prepare catalytically active Janus colloids that "swim" in fluids and describe how to determine their 3D motion using fluorescence microscopy. One commonly deployed method for catalytically active colloids to produce enhanced motion is via an asymmetrical distribution of catalyst. Here this is achieved by spin coating a dispersed layer of fluorescent polymeric colloids onto a flat planar substrate, and then using directional platinum vapor deposition to half coat the exposed colloid surface, making a two faced "Janus" structure. The Janus colloids are then re-suspended from the planar substrate into an aqueous solution containing hydrogen peroxide. Hydrogen peroxide serves as a fuel for the platinum catalyst, which is decomposed into water and oxygen, but only on one side of the colloid. The asymmetry results in gradients that produce enhanced motion, or "swimming". A fluorescence microscope, together with a video camera is used to record the motion of individual colloids. The center of the fluorescent emission is found using image analysis to provide an x and y coordinate for each frame of the video. While keeping the microscope focal position fixed, the fluorescence emission from the colloid produces a characteristic concentric ring pattern which is subject to image analysis to determine the particles relative z position. In this way 3D trajectories for the swimming colloid are obtained, allowing swimming velocity to be accurately measured, and physical phenomena such as gravitaxis, which may bias the colloids motion to be detected.

A method to prepare catalytically active Janus colloids that can "swim" in fluids and determine their 3D trajectories is presented.

We report a method to prepare catalytically active Janus colloids that "swim" in fluids and describe how to determine their 3D motion using fluorescence ...

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each thermoplastic of interest. Solvent bonding is a simple and versatile method that can be used to fabricate devices from a variety of plastics. An appropriate solvent is added between two device layers to be bonded, and heat and pressure are applied to the device to facilitate the bonding. By using an appropriate combination of solvent, plastic, heat, and pressure, the device can be sealed with a high quality bond, characterized as having high bond coverage, bond strength, optical clarity, durability over time, and low deformation or damage to microfeature geometry. We describe the procedure for bonding devices made from two popular thermoplastics, poly(methyl-methacrylate) (PMMA), and cyclo-olefin polymer (COP), as well as a variety of methods to characterize the quality of the resulting bonds, and strategies to troubleshoot low quality bonds. These methods can be used to develop new solvent bonding protocols for other plastic-solvent systems.

Solvent bonding is a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. We describe a protocol to achieve strong, optically clear bonds in PMMA and COP microfluidic devices that preserve microfeature details, by a judicious combination of pressure, temperature, an appropriate solvent, and device geometry.

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each ...

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

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

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

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

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