Name: solvent bonding for fabrication of pmma and cop microfluidic devices
Uploaded: 2017-01-17T15:00:00
Description: Watch this Scientific Journal Video about Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices at JoVE.com

We acknowledge financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC, #436117-2013), the Cancer Research Society (CRS, #20172), Myeloma Canada, and Grand Challenges Canada.

Note that all of the steps described below have been developed and performed in a non-cleanroom environment. The solvent bonding steps can certainly be performed in a cleanroom, if available, but this is not required.
1. Preparation of Thermoplastic Microfluidic Device Layers
<ol>
	<li>Design and fabricate microfluidic device layers from the thermoplastic of choice, using an appropriate fabrication method (e.g., micromilling15, embossing16-18</s...

<ol>
	<li>Beebe, D. J., Mensing, G. A., Walker, 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=Physics+and+applications+of+microfluidics+in+biology.">Physics and applications of microfluidics in biology.</a> Annual Review of Biomedical Engineering. 4, 261-286 (2002).</li><li>Situma, C., Hashimoto, M., Soper, 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=Merging+microfluidics+with+microarray-based+bioassays.">Merging microfluidics with microarray-based bioassays.</a> Biomolecular Engineering. 23 (5), 213-231 (2006).</li><li>Paguirigan, A. L., Beebe, D. 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K., Berthier, E., 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=Rapid+prototyping+of+arrayed+microfluidic+systems+in+polystyrene+for+cell-based+assays.">Rapid prototyping of arrayed microfluidic systems in polystyrene for cell-based assays.</a> Analytical Chemistry. 83 (4), 1408-1417 (2011).</li><li>Truckenm&#252;ller, R., Henzi, P., Herrmann, D., Saile, V., Schomburg, W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bonding+of+polymer+microstructures+by+UV+irradiation+and+subsequent+welding+at+low+temperatures.">Bonding of polymer microstructures by UV irradiation and subsequent welding at low temperatures.</a> Microsystem Technologies. 10 (5), 372-374 (2004).</li><li>Tsao, C. W., Hromada, L., Liu, J., Kumar, P., DeVoe, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low+temperature+bonding+of+PMMA+and+COC+microfluidic+substrates+using+UV/ozone+surface+treatment.">Low temperature bonding of PMMA and COC microfluidic substrates using UV/ozone surface treatment.</a> Lab on a Chip. 7 (4), 499-505 (2007).</li><li>Wan, A. M. D., Sadri, A., Young, E. W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liquid+phase+solvent+bonding+of+plastic+microfluidic+devices+assisted+by+retention+grooves.">Liquid phase solvent bonding of plastic microfluidic devices assisted by retention grooves.</a> Lab on a Chip. 15 (18), 3785-3792 (2015).</li><li>Guckenberger, D. J., de Groot, T. E., Wan, A. M. D., Beebe, D. J., Young, E. W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micromilling:+a+method+for+ultra-rapid+prototyping+of+plastic+microfluidic+devices.">Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices.</a> Lab on a Chip. 15 (11), 2364-2378 (2015).</li><li>Cameron, N. S., Roberge, H., Veres, T., Jakeway, S. C., John Crabtree, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+fidelity,+high+yield+production+of+microfluidic+devices+by+hot+embossing+lithography:+rheology+and+stiction.">High fidelity, high yield production of microfluidic devices by hot embossing lithography: rheology and stiction.</a> Lab on a Chip. 6 (7), 936 (2006).</li><li>Yang, S., Devoe, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+device+fabrication+by+thermoplastic+hot-embossing.">Microfluidic device fabrication by thermoplastic hot-embossing.</a> Methods in Molecular Biology. 949, 115-123 (2013).</li><li>Konstantinou, D., Shirazi, A., Sadri, A., Young, E. W. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combined+hot+embossing+and+milling+for+medium+volume+production+of+thermoplastic+microfluidic+devices.">Combined hot embossing and milling for medium volume production of thermoplastic microfluidic devices.</a> Sensors and Actuators B: Chemical. 234, 209-221 (2016).</li><li>Maszara, W. P., Goetz, G., Caviglia, A., McKitterick, J. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bonding+of+silicon+wafers+for+silicon-on-insulator.">Bonding of silicon wafers for silicon-on-insulator.</a> Journal of Applied Physics. 64 (10), 4943 (1988).</li><li>Bhattacharyya, A., Klapperich, 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=Mechanical+and+chemical+analysis+of+plasma+and+ultraviolet-ozone+surface+treatments+for+thermal+bonding+of+polymeric+microfluidic+devices.">Mechanical and chemical analysis of plasma and ultraviolet-ozone surface treatments for thermal bonding of polymeric microfluidic devices.</a> Lab on a Chip. 7 (7), 876-882 (2007).</li></ol>

The feasibility of potential bonding strategies depends on available equipment. While hotplates are relatively common and free weights can be purchased inexpensively, high pressure strategies will require the use of a heated press. For example, our optimal PMMA bonding recipe requires high pressure to bond with ethanol (see Table 1), and the required pressure is not attainable for typical device sizes using free weights. Thus, if only a hotplate and weights are available, PMMA can instead be bonded with ...

Microfluidics has emerged over the past twenty years as a technology well suited for studying chemistry and physics at the microscale1, and with growing promise to significantly contribute to biology research2-4. The majority of microfluidic devices have historically been made from poly(dimethylsiloxane) (PDMS), a silicone elastomer that is easy to use, inexpensive, and offers high quality feature replication5. However, PDMS has well-documented shortcomings and is incompatible with high-volume fabrication processes6,7, and as such, there has been a growing trend toward fabricating microfluidic devices from thermoplastic materials, because of their potential for mass manufacturing and thus commercialization.
One of the major barriers to wider adoption of plastic microfabrication has been achieving easy, high quality bonding of plastic devices. Current strategies employ thermal, adhesive, and solvent bonding techniques, but many suffer from significant challenges. Thermal bonding increases autofluorescence8 and often deforms microchannel geometries9-11, while adhesive techniques require stencils, careful alignment, and ultimately leave the thickness of the adhesive exposed to the microchannel10. Solvent bonding is attractive due to its simplicity, tunability, and low cost10,12-14. In particular, its tunability enables optimization for a variety of plastics, which can yield consistent, high quality bonding that minimizes deformation of microfeatures14.
During solvent bonding, solvent exposure increases the mobility of polymer chains near the surface of the plastic, which enables inter-diffusion of chains across the bonding interface. This causes entanglement via mechanical interlocking of the diffusing chains, and results in a physical bond10. Thermal bonding works in a similar manner, but relies on elevated temperature alone to increase chain mobility. Thus, thermal methods require temperatures near or above the glass transition of the polymer, whereas the use of solvents can significantly reduce the temperature needed for bonding, and thus reduce unwanted deformation.
We provide a specific protocol for bonding both PMMA and COP devices. However, this protocol and method describes a simple, generic approach for solvent bonding of thermoplastic microfluidic devices that can be tailored for other plastic materials, solvents, and available equipment. We describe numerous methods for assessing the quality of bonds (e.g., bond coverage, bond strength, bond durability, and deformation of microfeature geometries), and provide troubleshooting approaches to address these common challenges.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>COP</td>
			<td>Zeonor</td>
			<td>604Z1020R080</td>
			<td>20 kg COP Pellets - 1020R. Multiple suppliers can be used, but may affect bonding characteristics.</td>
		</tr>
		<tr>
			<td>PMMA</td>
			<td>McMaster Carr</td>
			<td>8560K173</td>
			<td>1.5 mm sheet thickness for our typical applications. Multiple suppliers can be used, but may affect bonding characteristics.</td>
		</tr>
		<tr>
			<td>Cyclohexane</td>
			<td>Sigma-Aldrich</td>
			<td>227048</td>
			<td>Cyclohexane, anhydrous, 99.5%. Multiple suppliers can be used. Toxic, requires fumehood.</td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>24102</td>
			<td>Ethanol, absolute, &#8805;99.8% (GC). Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Sigma-Aldrich</td>
			<td>179124</td>
			<td>Acetone, ACS reagent, &#8805;99.5%. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>2-Propanol</td>
			<td>Sigma-Aldrich</td>
			<td>278475</td>
			<td>2-Propanol, anhydrous, 99.5%. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Hot plate(s)</td>
			<td>Torrey Pines Scientific</td>
			<td>HP60</td>
			<td>Fully programmable digital hotplate. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Free weights</td>
			<td>Cap Barbell</td>
			<td>RPG#2</td>
			<td>Standard cast iron plate. Multiple suppliers and different weights can be used.</td>
		</tr>
		<tr>
			<td>Heated press</td>
			<td>Carver</td>
			<td>Auto CH</td>
			<td>Auto series heated hydraulic press. Multiple suppliers can be used. A press that fits in a fumehood would allow the most flexibility (this model does not).</td>
		</tr>
		<tr>
			<td>CNC Milling Machine</td>
			<td>Tormach</td>
			<td>PCNC 770</td>
			<td>3 Axis CNC mill. Multiple suppliers can be used.</td>
		</tr>
		<tr>
			<td>Endmills</td>
			<td>Various</td>
			<td>Various</td>
			<td>Required sizes depend on designs. Multiple suppliers can be used.</td>
		</tr>
	</tbody>
</table>

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.

A schematic of the general solvent bonding procedure is shown in Figure 1. The easiest way to assess bond quality is to visually inspect bond coverage, since poor bond coverage is easily visible as regions of unbonded plastic, and is indicative of weak bonding. Such regions are typically near free edges (e.g., periphery of device, or near open ports or microchannels), and can also often appear around any particles of dirt or dust at the bonding interface. Poor bo...

Watch this Scientific Journal Video about Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices at JoVE.com

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

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 ...

The overall goal of this technique is to provide a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. This solvent bonding procedure will allow us to fabricate well bonded and durable thermoplastic microfluidic devices for a variety of applications from microfluidic cell culture systems to prototypes for point of care diagnostic tools. The main advantage of this technique is that it allows us to quickly and easily bond thermoplastic device layers.The procedure can be easily adapted to bond different thermoplastic materials. Design and fabricate microfluidic device layers from the thermoplastic of choice, using an appropriate fabrication method. Visually inspect the device layers to ensure that edges are clean without burrs or ridges of leftover material from the fabrication process.For best results, check all machined microfeature edges, in addition to the outside edges of the device, under an optical microscope. If leftover material is found during visual inspection, use a razor blade or scalpel to carefully remove any material that prevents the device layers from lying flat against one another so that the interfaces of the layers come into conformal contact. Then, clean the device surfaces with laboratory soap and water.And, dry with compressed air. After submerging the device layers in 2-propanol for two minutes, dry them with compressed air. This video is demonstrated with poly methyl methacrylate, abbreviated PMMA.Please see the text protocol for slight alterations in the procedure when using cyclic olefin polymer, or COP. Preheat, a heated press to 70 degrees celsius and allow the temperature to stabilize. To prepare the solvent for bonding process, measure 0.5 milliliters of ethanol, per square inch of bonding area for PMMA.It's important that an appropriate volume of solvent is applied to the device layers because too much solvent can lead to challenges in aligning layers. Dispense 0.1 milliliters of solvent per square inch of bonding area between cleaned plastic layers and bring the layers together. Visually inspect the bonding interface for air bubbles, which are common and should be removed as much as possible.If bubbles are present, slide the two plastic layers along the bonding interface so that they nearly come apart. And, then, slide them back together. To align the layers of the device by hand, use fingers to align the outer edges of the device.If more accurate alignment is required, include L shaped corner brackets to hold the device layers together. Next, place the device with solvent into the preheated press and apply 2, 300 kPa of pressure for two minutes. Use tweezers to safely remove the hot device for inspection.Bonding is now complete. Finally, remove any remaining liquid in the device using compressed air. Shown here are representative results of a pair of device layers before cleaning and after cleaning.The device layers have been milled to remove burrs. A representative image of a device with solvent added shows bubbles present through the bonding surface that can inhibit bonding. Conversely, well distributed solvent that is free of bubbles leads to strong, high quality bonds.Rapid solvent evaporation, during heating, can lead to regions of unbonded material near free edges of the device, resulting in poor bond coverage, leaky microfluidic features, and low overall bond strength. These regions are visible as lighter patches with colored interference fringes. An optimized solvent plastic system achieves good bond coverage and strength and minimizes damage to microfeatures, while still properly sealing them.Once mastered, a new thermoplastic device design can be fabricated in as little as two hours if the bonding technique is done properly. Remember that working with cyclohexane can be hazardous and should be handled in a fume hood and while wearing personal protective equipment. After watching this video, you will have a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds that are leak free and appropriate for use in cell culture, in point of care diagnostic applications.

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Engineering

Fabrication of Uniform Nanoscale Cavities via Silicon Direct Wafer Bonding

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned and bonded silicon wafers. Unlike confinements in porous materials often used for these types of experiments3, bonded wafers provide predesigned uniform spaces for confinement. The geometry of each cell is well known, which removes a large source of ambiguity in the interpretation of data.
Exceptionally flat, 5 cm diameter, 375 &#181;m thick Si wafers with about 1 &#181;m variation over the entire wafer can be obtained commercially (from Semiconductor Processing Company, for example). Thermal oxide is grown on the wafers to define the confinement dimension in the z-direction. A pattern is then etched in the oxide using lithographic techniques so as to create a desired enclosure upon bonding. A hole is drilled in one of the wafers (the top) to allow for the introduction of the liquid to be measured. The wafers are cleaned2 in RCA solutions and then put in a microclean chamber where they are rinsed with deionized water4. The wafers are bonded at RT and then annealed at ~1,100 &#176;C. This forms a strong and permanent bond. This process can be used to make uniform enclosures for measuring thermal and hydrodynamic properties of confined liquids from the nanometer to the micrometer scale.

A method for permanently bonding two silicon wafers so as to realize a uniform enclosure is described. This includes wafer preparation, cleaning, RT bonding, and annealing processes. The resulting bonded wafers (cells) have uniformity of enclosure ~1%1,2. The resulting geometry allows for measurements of confined liquids and gasses.

Measurements of the heat capacity and superfluid fraction of confined 4He have been performed near the lambda transition using lithographically patterned ...

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 ...

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&#8217;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&#39;s electronic structure in the presence of a charged impurity.&#160;The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&#8217;s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

This paper details the fabrication process of a gate-tunable graphene device, decorated with Coulomb impurities for scanning tunneling microscopy studies. Mapping the spatially dependent electronic structure of graphene in the presence of charged impurities unveils the unique behavior of its relativistic charge carriers in response to a local Coulomb potential.

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees ...

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 and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

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 ...

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 ...

Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for applications in two-dimensional nanoelectronics devices. Although many methods to synthesize SnSe nanocrystals have been developed, a simple way to fabricate large-sized single-layer SnSe flakes remains a great challenge. Herein, we show the experimental method to directly grow large-sized single-layer rectangular SnSe flakes on commonly used SiO2/Si insulating substrates using a straightforward two-step fabrication method in an atmospheric pressure quartz tube furnace system. The single-layer rectangular SnSe flakes with an average thickness of ~6.8 &#197; and lateral dimensions of about 30 &#181;m &#215; 50 &#181;m were fabricated by a combination of vapor transport deposition technique and nitrogen etching route. We characterized the morphology, microstructure, and electrical properties of the rectangular SnSe flakes and obtained excellent crystallinity and good electronic properties. This article about the two-step fabrication method can help researchers grow other similar two-dimensional, large-sized, single-layer materials using an atmospheric pressure system.

A protocol is presented demonstrating a two-step fabrication technique to grow large-sized single-layer rectangular shaped SnSe flakes on low-cost SiO2/Si dielectrics wafers in an atmospheric pressure quartz tube furnace system.

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for ...

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. This paper proposes a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation. The polydimethylsiloxane (PDMS) chip was fabricated using the multi-layer soft lithography method. Hexadecane containing surfactant was used as the continuous phase, and PEGDA with the ultraviolet (UV) photo-initiator was the dispersed phase. Surfactants allowed the local surface tension to drop and formed a more cusped tip which promoted breaking into tiny micro-droplets. As the pressure of dispersed phase was constant, the size of droplets became smaller with increasing continuous phase pressure before dispersed phase flow was broken off. As a result, droplets with size variation from 1 &#181;m to 80 &#181;m in diameter could be selectively achieved by changing the pressure ratio in two inlet channels, and the average coefficient of variation was estimated to be below 7%. Furthermore, droplets could turn into micro-beads by UV exposure for photo-polymerization. Conjugating biomolecules on such micro-beads surface have many potential applications in the fields of biology and chemistry.

Generation of Size-controlled Poly ethylene Glycol Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Here, we present a protocol to illustrate the fabrication processes and verifying experiments of a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation.

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. ...

Fabrication of Refractive-index-matched Devices for Biomedical Microfluidics

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices can be implemented as part of a robust platform capable of making simultaneous complementary measurements. The primary challenge created by the combination of these two techniques is the mismatch in refractive index between the materials traditionally used to make microfluidic devices and the aqueous solutions typically used in biomedicine. This mismatch can create optical artifacts near the channel or device edges. One solution is to reduce the refractive index of the material used to fabricate the device by using a fluorinated polymer such as MY133-V2000 whose refractive index is similar to that of water (n = 1.33). Here, the construction of a microfluidic device made out of MY133-V2000 using soft lithography techniques is demonstrated, using O2 plasma in conjunction with an acrylic holder to increase the adhesion between the MY133-V2000 fabricated device and the polydimethylsiloxane (PDMS) substrate. The device is then tested by incubating it filled with cell culture media for 24 h to demonstrate the ability of the device to maintain cell culture conditions during the course of a typical imaging experiment. Finally, quantitative phase microscopy (QPM) is used to measure the distribution of mass within the live adherent cells in the microchannel. This way, the increased precision, enabled by fabricating the device from a low index of refraction polymer such as MY133-V2000 in lieu of traditional soft lithography materials such as PDMS, is demonstrated. Overall, this approach for fabricating microfluidic devices can be readily integrated into existing soft lithography workflows in order to reduce optical artifacts and increase measurement precision.

This protocol describes the fabrication of microfluidic devices from MY133-V2000 to eliminate artifacts that often arise in microchannels due to the mismatching refractive indices between microchannel structures and an aqueous solution. This protocol uses an acrylic holder to compress the encapsulated device, improving adhesion both chemically and mechanically.

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices ...