The authors are grateful for the support of the National Science Foundation under Grant No. CMMI-00748094 and the ONR N000141110629.

The protocol text is broken up into three main sections: 1) the fabrication of the of the PDMS (polydimethylsiloxane) pillars, 2) the functionalization of the tops of the pillars, and 3) the formation and characterization of the capillary bridges.
1. Fabrication of the PDMS Pillars
This section details the fabrication of the PDMS pillars using die casting with a silicon/SU-8 mold.
<ol>
	<li>Fabrication of silicon/SU-8 mold
	<ol>
		<li>Place a clean 4 in silicon wafer in a Pyrex Petri dish.</li>
		<li>Prepare a 4:1 (by volume) sulfuric acid to hydrogen peroxide (piranha) solution in a separate beaker. 
		Note: Extreme caution is needed in the preparation and use of the piranha solution. The reaction is highly exothermic and insulated gloves will be required to handle beakers. Piranha reacts violently with organics. Let piranha solution cool to room temperature before disposing. Only prepare enough solution required to submerge the wafer in the dish.</li>
		<li>Pour piranha solution slowly onto the silicon wafer until it is completely submerged. Let sit for 15 min.</li>
		<li>Remove the wafer from the Petri dish and rinse under a stream of: deionized (DI) water for 2 min, ethanol for 30 sec, acetone for 30 sec, then blow dry with nitrogen. 
		Note: If residues from acetone are a problem, an additional rinse with IPA is recommended</li>
		<li>Dry the wafer on a hot plate at 150 &#176;C for 15 min.</li>
		<li>Remove from hot plate and let cool to room temperature.</li>
		<li>Spin coat SU-8 2002 onto the surface of the wafer for 40 sec at 500 rpm.</li>
		<li>Spin coat SU-8 2050 onto the wafer with a two-step spin coater program. Step 1: 40 sec at 500 rpm. Step 2: 1 min at 1,500 rpm.</li>
		<li>Remove the wafer from the spin coater and place on a preheated hotplate (65 &#176;C) for 10 min.</li>
		<li>Let cool to room temperature, then place mask over wafer.</li>
		<li>Place under ultraviolet lamp and expose for 30 sec at 200 watts.</li>
		<li>Remove mask and place the wafer on a preheated hotplate (95 &#176;C) for 10 min.</li>
		<li>Place in SU-8 Developer solution and lightly agitate until all unexposed SU-8 has been removed. Then rinse in a stream of isopropyl alcohol for 30 sec, blow dry with nitrogen.</li>
		<li>Place on a preheated hotplate (95 &#176;C) for 30 min for a final hardbake.</li>
	</ol>
	</li>
	<li>Die casting of PDMS pillars
	<ol>
		<li>Mix vigorously a 10:1 mass ratio of PDMS sylgard-184 base to curing agent in beaker.</li>
		<li>Degas PDMS in a vacuum chamber until all bubbles are gone.</li>
		<li>Place the mold fabricated in section 1.1 in a large 4 in plastic weighing dish and pour the PDMS.</li>
		<li>Place dish with PDMS and mold back into vacuum chamber. Degas again until all bubbles are gone.</li>
		<li>Place entire dish in an oven (preheated to 75 &#176;C) for at least 2 hr. Then let cool to room temperature.</li>
		<li>Cut away the dish from the PDMS, and the PDMS from the silicon wafer with a straight razor blade.</li>
		<li>Cut out PDMS region with the pillars from the bulk and store in a clean Petri dish.</li>
	</ol>
	</li>
</ol>
2. Functionalization of the Tops of the Pillars
This three-step process involves first the evaporation of a gold film on a silicon wafer, followed by imprint transfer lithography16 of the gold film onto the PDMS pillars (fabricated in section 1), and lastly the functionalization of the gold film with a self-assembled monolayer to render it hydrophilic.
<ol>
	<li>Fabrication of gold on silicon wafers for imprint transfer lithography 
	<ol>
		<li>Use a glass cutter to dice a 4 in circular silicon wafer into 4 equally sized pieces. Note: Wafers can be cleaned using steps 1.1.2-1.1.4 and reused.</li>
		<li>Evaporate 20 nm of gold directly onto the silicon wafer.</li>
		<li>Leave the wafer in evaporation chamber (or in a desiccator) until section 3 below is complete. This will keep the wafer as clean as possible.</li>
		<li>Prepare an 8 &#181;l:20 ml, (3-mercaptopropyl)-trimethoxysilane (MPTS) : toluene solution in a clean glass vial.</li>
		<li>Prepare 200 ml of 16 mM hydrochloric acid (HCl) in a clean beaker.</li>
		<li>Put the wafer with gold film into the plasma reactor.</li>
		<li>Clean the wafer using oxygen plasma at a pressure of 300 mTorr, power of 50 W for 10 min. 
		Note: For this procedure a home-built plasma reactor was used.</li>
		<li>Put the wafer in a Pyrex Petri dish full of 200 proof ethanol for at least 10 min. 
		Note: This step is done to remove any unstable oxides that form on the gold due to the oxygen plasma.</li>
		<li>Rinse the wafer with ethanol, then blow dry with nitrogen.</li>
		<li>Spin coat the MPTS solution onto the wafer at 500 rpm for 30 sec followed by 2,750 rpm for 1 min. 
		Note: MPTS is used as an adhesion layer between the PDMS and gold layer16.</li>
		<li>Take the wafer off of the spin coater and rinse under a stream of ethanol. Then, rinse with DI water and blow dry with nitrogen. 
		Note: Rinse gently to avoid peeling of the gold layer from the silicon wafer.</li>
		<li>Place the wafer into a Pyrex Petri dish that contains enough 16 mM HCl solution to fully submerge the wafer. Leave in HCl for at least 5 min. 
		Note: Place into the solution gently to prevent the gold from peeling off. 
		Note: This is done to improve the adhesion between the PDMS and gold layer16.</li>
		<li>Remove the wafer from the HCl solution and blow dry with nitrogen. 
		Note: wafers should be used no more than 15-20 min after this step is complete.</li>
	</ol>
	</li>
	<li>Imprint transfer lithography of the gold from wafer to PDMS pillars
	<ol>
		<li>Prepare one 25 mm x 75 mm glass slide for each PDMS sample by rinsing it with ethanol, DI water, and blow dry with nitrogen.</li>
		<li>Place PDMS pillars into plasma chamber and perform oxygen plasma at a pressure of 300 mTorr and power of 50 W for 30 sec. 
		Note: overexposure of the PDMS to the oxygen plasma will cause cracking. Adjust the plasma conditions accordingly.</li>
		<li>Bind the back of the PDMS substrates to the clean glass slides by applying light pressure to them. The glass slide facilitates the manipulations of the PDMS pillars and mounting on the device described in step 3.</li>
		<li>Flip the glass-backed PDMS substrates and press the pillars down onto the MPTS-functionalized gold films (step 2.1). Apply moderate pressure initially, and then put a weight (approximately 100 g) on the glass slide to ensure conformal contact.</li>
		<li>Leave the substrate in contact with the silicon wafer for at least 12 hr.</li>
		<li>Separate the PDMS substrate from the wafer. If the PDMS substrate is stuck, use a straight razor blade to carefully pry an edge of the PDMS off of the wafer.</li>
		<li>At this point a uniform gold film should be present on the top of the PDMS pillars. Use an optical microscope to verify that the gold film is not cracked or that there are no parts missing along the pillar.</li>
	</ol>
	</li>
	<li>Functionalization of the gold on the top of the PDMS pillars
	<ol>
		<li>Prepare enough 1 mM mercaptohexadecanoic acid (MHA) in dimethyl sulfoxide (DMSO) to submerge fully the gold on top of the PDMS pillars. 
		Note: DMSO is used for its low PDMS swelling factor17.</li>
		<li>Place the PDMS substrates in the MHA solution and keep them there for at least 24 hr.</li>
		<li>Remove the substrate from the MHA solution and rinse with DI water, then blow dry with nitrogen.</li>
		<li>Place in vacuum chamber (pressure &#60; 100 mTorr at 25 &#176;C) for at least 12 hr.</li>
	</ol>
	</li>
</ol>
Note: To verify that the functionalization process was successful, step 2 can be performed on a bulk piece of PDMS (without pillars) and the wetting angle can be tested in a goniometer. The MHA gold films should have advancing and receding water contact angles of &#60;15&#176; and ~0&#176;, respectively.18
3. Formation and Characterization of the Capillary Bridges
This section details how a liquid bridge can be introduced between two substrates followed by its characterization via imaging at different heights and fluid volumes.
<ol>
	<li>Using two pillar substrates (made in steps 1-2), place one in the top and one in the bottom holders. Secure the substrates using side tension screws. 
	Note: see Figure 1 and representative results for device details.</li>
	<li>Assemble the device by attaching the top substrate stage to the bread board such that the top substrate is roughly above the bottom substrate. Decrease the height between the two facing pillars to about 1mm.</li>
	<li>Rough alignment: using the x, y, and rotation knobs on the bottom substrate stage align (by eye) the gold strips for the two substrates so that they are parallel (looking top down through the top substrate).</li>
	<li>Fine alignment: position the camera to look down the length of the PDMS pillar. Using the live camera feed on the computer screen, further adjust the position of the bottom substrate so the pillars are parallel.</li>
	<li>Move the camera to the opposite side of the device and repeat step 3.4.</li>
	<li>Decrease the separation between the two pillars until the top pillar makes contact with the bottom pillar (using live camera feed). Zero the digital micro stage. This will be defined as a pore height of zero.</li>
	<li>Increase the pore height to approximately 200 &#181;m.</li>
	<li>Prepare a syringe with 1-5 &#181;l&#160;of an 80% glycerol, 20% water solution. Attach a 30 G&#160;needle to the end of the syringe, making sure no air bubbles get trapped inside the needle. 
	Note: the water/glycerol mixture is used to reduce evaporation during the experiment. Water can also be employed.</li>
	<li>Mount the syringe to the syringe xyz translation stage with a mechanical clamp.</li>
	<li>Adjust the micrometers on the syringe positioning stage so that the needle fits into the slit pore (parallel to the length of the pillars).</li>
	<li>Decrease the slit pore height so that the top and bottom surfaces gently contact the needle. This will make sure that the liquid will touch both surfaces and spontaneously form a capillary bridge.</li>
	<li>Dispense the liquid from the syringe into the slit pore slowly.</li>
	<li>Use the micrometers on the syringe positioning stage to remove the needle from the slit pore. 
	Note: At this point, the height of the slit pore can be varied and the liquid bridge imaged. 
	Note: The pictures can be analyzed with the open source software package ImageJ.</li>
</ol>

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	<li>Broesch, D. J., Frechette, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=From+Concave+to+Convex:+Capillary+Bridges+in+Slit+Pore+Geometry.">From Concave to Convex: Capillary Bridges in Slit Pore Geometry.</a> Langmuir. 28, 15548-15554 (2012).</li><li>Orr, F. M., Scriven, L. E., Rivas, A. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pendular+rings+between+solids+-+meniscus+properties+and+capillary+force.">Pendular rings between solids - meniscus properties and capillary force.</a> J. Fluid Mech. 67, 723-742 (1975).</li><li>Rose, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Volumes+and+surface+areas+of+pendular+rings.">Volumes and surface areas of pendular rings.</a> J. Appl. 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Authors have nothing to disclose.

The method presented here provides a way to create capillary bridges in slit pore geometry, and also a method for imaging these bridges so that their morphology can be analyzed and compared to simulation and theory.
This method incorporates physical relief as well as selective chemical patterning to create asymmetric wetting properties. If only a chemical heterogeneity is present, a liquid drop will stay pinned on the heterogeneity until the contact angle exceeds that of the less wettable (low...

The study of the shape and resulting forces caused by capillary bridges has been the subject of extensive studies2-7. Initially most efforts were focused, due to their simplicity, on axisymmetric capillary bridges. Often capillary bridges occurring in natural systems, such as those found in granular and porous media8,9&#160;and bridges employed in technological applications, such as for capillary self-assembly in flip chip technologies10-15 are asymmetric with nonuniform wetting properties on the interacting surfaces. The combination of improved lithography techniques along with the accessibility of simple numerical tools to model fluid interfaces allows for the creation and modeling of capillary bridges with increasing complexity.
Capillary bridges in slit-pore geometry offer an interesting compromise: the directional wetting properties lead to nonaxisymmetric bridges that retain some symmetry planes (which simplifies the analysis). They have been studied theoretically and numerically as a case study for porous media. Systematic experimental studies of capillary bridges in slit-pore geometry have, however, been limited. Here we present a method to create and characterize capillary bridges in slit pore geometry. Briefly, the method consists of 1) the fabrication of pillars to create a chemical and physical heterogeneity, 2) the design of a microstage to align and manipulate the bridges, and 3) the imaging of the capillary bridges either from the front or the sides to characterize their morphology. The characterization of the bridge morphology, along with comparisons to surface evolver simulations are provided in a separate publication1.

<table border="0" cellpadding="0" cellspacing="0" width="425">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">99.999% Gold wire</td>
			<td style="width:84px;">Kurt J. Lesker</td>
			<td style="width:91px;">EVMAU40040</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Acetone</td>
			<td style="width:84px;">Pharmco-AAPER</td>
			<td style="width:91px;">C1107283</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:167px;">Dimethyl sulfoxide</td>
			<td style="width:84px;">Fisher</td>
			<td style="width:91px;">D128-500</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Ethanol (200 proof)</td>
			<td style="width:84px;">Pharmco-AAPER</td>
			<td style="width:91px;">111000200</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Hydrochloric acid</td>
			<td style="width:84px;">EMD</td>
			<td style="width:91px;">HX0603-4</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Hydrogen peroxide (30%)</td>
			<td style="width:84px;">EMD</td>
			<td style="width:91px;">HX0635-3</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Isopropyl alcohol</td>
			<td style="width:84px;">Fisher</td>
			<td style="width:91px;">L-13597</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Mercapto hexadecanoic acid (90%)</td>
			<td style="width:84px;">Sigma-Aldrich</td>
			<td style="width:91px;">448303-1G</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:167px;">Mercapto-propyl-trimethoxy-silane (MPTS)</td>
			<td style="width:84px;">Gelest</td>
			<td style="width:91px;">Sim6476-O-100GM</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:167px;">Milli-Q DI water</td>
			<td style="width:84px;">Millipore</td>
			<td style="width:91px;">Milli-Q</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Nitrogen (gas)</td>
			<td style="width:84px;">Airgas</td>
			<td style="width:91px;">UN1066</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Oxygen (gas)</td>
			<td style="width:84px;">Airgas</td>
			<td style="width:91px;">UN1072</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Silicon wafers (4 in)</td>
			<td style="width:84px;">WRS Materials</td>
			<td style="width:91px;">CC8506</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">SU-8 2002 (negative photo resist)</td>
			<td style="width:84px;">MicroChem</td>
			<td style="width:91px;">SU82002</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">SU-8 2050 (negative photoresist)</td>
			<td style="width:84px;">MicroChem</td>
			<td style="width:91px;">SU82050</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">SU-8 Developer solution</td>
			<td style="width:84px;">MicroChem</td>
			<td style="width:91px;">Y020100 4000L1PE</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:167px;">Sulfuric acid</td>
			<td style="width:84px;">J.T. Baker</td>
			<td style="width:91px;">9681-03</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:167px;">Poly dimethy sulfoxide (PDMS)</td>
			<td style="width:84px;">Dow Corning</td>
			<td style="width:91px;">Sylgard -184</td>
			<td style="width:84px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:167px;">Toluene</td>
			<td style="width:84px;">Omnisolv</td>
			<td style="width:91px;">TX0737-1</td>
			<td style="width:84px;">
			
			</td>
		</tr>
	</tbody>
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fabrication and visualization of capillary bridges in slit pore geometry

A procedure for creating and imaging capillary bridges in slit-pore geometry is presented. High aspect ratio hydrophobic pillars are fabricated and functionalized to render their top surfaces hydrophilic. The combination of a physical feature (the pillar) with a chemical boundary (the hydrophilic film on the top of the pillar) provides both a physical and chemical heterogeneity that pins the triple contact line, a necessary feature to create stable long but narrow capillary bridges. The substrates with the pillars are attached to glass slides and secured into custom holders. The holders are then mounted onto four axis microstages and positioned such that the pillars are parallel and facing each other. The capillary bridges are formed by introducing a fluid in the gap between the two substrates once the separation between the facing pillars has been reduced to a few hundred micrometers. The custom microstage is then employed to vary the height of the capillary bridge. A CCD camera is positioned to image either the length or the width of the capillary bridge to characterize the morphology of the fluid interface. Pillars with widths down to 250 &#181;m and lengths up to 70 mm were fabricated with this method, leading to capillary bridges with aspect ratios (length/width) of over 1001.

Description of the experimental device
The experimental device can be broken up into four main parts: 1) the top substrate stage, 2) the bottom substrate stage, 3) the syringe/ syringe xyz-translation stage and 4) the camera/optics and camera holder. The details of each follow:
<ol>
	<li>Top substrate stage. A digital translation stage is attached to a P-series mounting clamp via a custom machined connector piece. The mounting clamp is connected to a variable height P-post, w...

Watch this Scientific Journal Video about Fabrication and Visualization of Capillary Bridges in Slit Pore Geometry at JoVE.com

Fabrication and Visualization of Capillary Bridges in Slit Pore Geometry

A procedure for creating and imaging capillary bridges in slit-pore geometry is presented. The creation of capillary bridges relies on the formation of pillars to provide a directional physical and chemical heterogeneity to pin the fluid. Capillary bridges are formed and manipulated using microstages and visualized using a CCD camera.

A procedure for creating and imaging capillary bridges in slit-pore geometry is presented. High aspect ratio hydrophobic pillars are fabricated and ...

fabrication-visualization-capillary-bridges-slit-pore

Research

JoVE Journal

Engineering

6.4K Views.  Johns Hopkins University. A procedure for creating and imaging capillary bridges in slit-pore geometry is presented. The creation of capillary bridges relies on the formation of pillars to provide a directional physical and chemical heterogeneity to pin the fluid. Capillary bridges are formed and manipulated using microstages and visualized using a CCD camera.

Video: Fabrication and Visualization of Capillary Bridges in Slit Pore Geometry

Fabrication And Characterization Of Photonic Crystal Slow Light Waveguides And Cavities

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view and for its considerable potential for practical applications. Slow light photonic crystal waveguides, in particular, have played a major part and have been successfully employed for delaying optical signals1-4 and the enhancement of both linear5-7 and nonlinear devices.8-11
Photonic crystal cavities achieve similar effects to that of slow light waveguides, but over a reduced band-width. These cavities offer high Q-factor/volume ratio, for the realization of optically12 and electrically13 pumped ultra-low threshold lasers and the enhancement of nonlinear effects.14-16 Furthermore, passive filters17 and modulators18-19 have been demonstrated, exhibiting ultra-narrow line-width, high free-spectral range and record values of low energy consumption.
To attain these exciting results, a robust repeatable fabrication protocol must be developed. In this paper we take an in-depth look at our fabrication protocol which employs electron-beam lithography for the definition of photonic crystal patterns and uses wet and dry etching techniques. Our optimised fabrication recipe results in photonic crystals that do not suffer from vertical asymmetry and exhibit very good edge-wall roughness. We discuss the results of varying the etching parameters and the detrimental effects that they can have on a device, leading to a diagnostic route that can be taken to identify and eliminate similar issues.
The key to evaluating slow light waveguides is the passive characterization of transmission and group index spectra. Various methods have been reported, most notably resolving the Fabry-Perot fringes of the transmission spectrum20-21 and interferometric techniques.22-25 Here, we describe a direct, broadband measurement technique combining spectral interferometry with Fourier transform analysis.26 Our method stands out for its simplicity and power, as we can characterise a bare photonic crystal with access waveguides, without need for on-chip interference components, and the setup only consists of a Mach-Zehnder interferometer, with no need for moving parts and delay scans.
When characterising photonic crystal cavities, techniques involving internal sources21 or external waveguides directly coupled to the cavity27 impact on the performance of the cavity itself, thereby distorting the measurement. Here, we describe a novel and non-intrusive technique that makes use of a cross-polarised probe beam and is known as resonant scattering (RS), where the probe is coupled out-of plane into the cavity through an objective. The technique was first demonstrated by McCutcheon et al.28 and further developed by Galli et al.29

Use of photonic crystal slow light waveguides and cavities has been widely adopted by the photonics community in many differing applications. Therefore fabrication and characterization of these devices are of great interest. This paper outlines our fabrication technique and two optical characterization methods, namely: interferometric (waveguides) and resonant scattering (cavities).

Slow light has been one of the hot topics in the photonics community in the past decade, generating great interest both from a fundamental point of view ...

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

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 ...

The Preparation of Electrohydrodynamic Bridges from Polar Dielectric Liquids

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and polar dielectric liquids. These bridges are unique from capillary bridges in that they exhibit extensibility beyond a few millimeters, have complex bi-directional mass transfer patterns, and emit non-Planck infrared radiation. A number of common solvents can form such bridges as well as low conductivity solutions and colloidal suspensions. The macroscopic behavior is governed by electrohydrodynamics and provides a means of studying fluid flow phenomena without the presence of rigid walls. Prior to the onset of a liquid bridge several important phenomena can be observed including advancing meniscus height (electrowetting), bulk fluid circulation (the Sumoto effect), and the ejection of charged droplets (electrospray). The interaction between surface, polarization, and displacement forces can be directly examined by varying applied voltage and bridge length. The electric field, assisted by gravity, stabilizes the liquid bridge against Rayleigh-Plateau instabilities. Construction of basic apparatus for both vertical and horizontal orientation along with operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical electrohydrodynamic liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields and polar dielectric liquids. The construction of basic apparatus and operational examples, including thermographic images, for three liquids (e.g., water, DMSO, and glycerol) is presented.

Horizontal and vertical liquid bridges are simple and powerful tools for exploring the interaction of high intensity electric fields (8-20 kV/cm) and ...

Atomically Traceable Nanostructure Fabrication

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

We report a protocol for combining the atomic metrology of the Scanning Tunneling Microscope for surface patterning with selective Atomic Layer Deposition and Reactive Ion Etching. Using a robust process involving numerous atmospheric exposures and transport, 3D nanostructures with atomic metrology are fabricated.

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process ...

Dynamic Pore-scale Reservoir-condition Imaging of Reaction in Carbonates Using Synchrotron Fast Tomography

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve geologic seals and allow CO2 to escape. However, the dissolution processes at reservoir conditions are poorly understood. Thus, time-resolved experiments are needed to observe and predict the nature and rate of dissolution at the pore scale. Synchrotron fast tomography is a method of taking high-resolution time-resolved images of complex pore structures much more quickly than traditional &#181;-CT. The Diamond Lightsource Pink Beam was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 hours. The images were segmented and the porosity and permeability were measured using image analysis and network extraction. Porosity increased uniformly along the length of the sample; however, the rate of increase of both porosity and permeability slowed at later times.

Synchrotron fast tomography was used to dynamically image dissolution of limestone in the presence of CO2-saturated brine at reservoir conditions. 100 scans were taken at a 6.1 &#181;m resolution over a period of 2 h.

Underground storage permanence is a major concern for carbon capture and storage. Pumping CO2 into carbonate reservoirs has the potential to dissolve ...

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 ...

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by the Washburn equation was considered equivalent to a flow under the effect of capillary pressure according to the Darcy law. Experimental tests for the characterization of wicking were conducted with both carbon and flax fiber reinforcement. Quasi-unidirectional fabrics were then tested by means of a tensiometer to determine the morphological and wetting parameters along the fiber direction. The procedure was shown to be promising when the morphology of the fabric is unchanged during capillary wicking. In the case of carbon fabrics, the capillary pressure can be calculated. Flax fibers are sensitive to moisture sorption and swell in water. This phenomenon has to be taken into account to assess the wetting parameters. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. This treatment enhances fiber morphological stability and prevents swelling in water. It was shown that treated fabrics have a linear wicking trend similar to those found in carbon fabrics, allowing for the determination of capillary pressure.

An experimental method to measure geometrical parameters and the apparent advancing contact angles describing capillary wicking in unidirectional synthetic and natural fabrics is proposed. These parameters are mandatory for the determination of the capillary pressures that must be taken into account for liquid composite molding (LCM) applications.

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify ...

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, interface precipitation, and mini-emulsion. In all methods, well-defined, micrometer-sized spheres are obtained from a self-assembling process in solution. The vapor diffusion method can result in spheres with the highest sphericity and surface smoothness, yet the types of the polymers able to form these spheres are limited. On the other hand, in the mini-emulsion method, microspheres can be made from various types of polymers, even from highly crystalline polymers with coplanar, &#960;-conjugated backbones. The photoluminescent (PL) properties from single isolated microspheres are unusual: the PL is confined inside the spheres, propagates at the circumference of the spheres via the total internal reflection at the polymer/air interface, and self-interferes to show sharp and periodic resonant PL lines. These resonating modes are so-called "whispering gallery modes" (WGMs). This work demonstrates how to measure WGM PL from single isolated spheres using the micro-photoluminescence (&#181;-PL) technique. In this technique, a focused laser beam irradiates a single microsphere, and the luminescence is detected by a spectrometer. A micromanipulation technique is then used to connect the microspheres one by one and to demonstrate the intersphere PL propagation and color conversion from coupled microspheres upon excitation at the perimeter of one sphere and detection of PL from the other microsphere. These techniques, &#181;-PL and micromanipulation, are useful for experiments on micro-optic application using polymer materials.

Protocols for the synthesis of microspheres from polymers, the manipulation of microspheres, and micro-photoluminescence measurements are presented.

This paper describes three methods of preparing fluorescent microspheres comprising &#960;-conjugated or non-conjugated polymers: vapor diffusion, ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...