Name: fabrication of polymer microspheres for optical resonator and laser applications
Uploaded: 2017-06-02T15:00:00
Description: Watch this Scientific Journal Video about Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications at JoVE.com

This work was partly supported by KAKENHI (25708020, 15K13812, 15H00860, 15H00986, 16H02081) from JSPS/MEXT Japan, the Asahi Glass Foundation, and the University of Tsukuba Pre-strategic initiative, "Ensemble of light with matters and life."

1. Fabrication Protocols of Polymer Microspheres
<ol>
	<li>Vapor Diffusion Method
	<ol>
		<li>Dissolve 2 mg of conjugated polymers, such as P1 (poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(5-octylthieno[3,4-c]pyrrole-4,6-dione-1,3-diyl)])28 and P2 (poly[(N-(2-heptylundecyl)carbazole-2,7-diyl)-alt-(4,8-bis[(dodecyl)carbonyl]benzo[1,2-b:4,5-b&#8242;]dithiophene-2,6-diyl)])28, in 2 mL of chloroform (a good solvent) in...

<ol>
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Actuators B. 136, 275-286 (2009).</li><li>Wu, C., Szymanski, C., Cain, Z., McNeill, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conjugated+Polymer+Dots+for+Multiphoton+Fluorescence+Imaging.">Conjugated Polymer Dots for Multiphoton Fluorescence Imaging.</a> J. Am. Chem. Soc. 129, 12904-12905 (2007).</li><li>Feng, L., Zhu, C., Yuan, H., Liu, L., Lv, F., Wang, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conjugated+Polymer+Nanoparticles:+Preparation,+Properties,+Functionalization+And+Biological+Applications.">Conjugated Polymer Nanoparticles: Preparation, Properties, Functionalization And Biological Applications.</a> Chem. Soc. Rev. 42, 6620-6634 (2013).</li><li>Pecher, J., Mecking, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoparticles+of+Conjugated+Polymers.">Nanoparticles of Conjugated Polymers.</a> Chem. Rev. 110, 6260-6279 (2010).</li><li>McGehee, M. D., Heeger, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Semiconducting+(Conjugated)+Polymers+as+Materials+for+Solid-State+Lasers.">Semiconducting (Conjugated) Polymers as Materials for Solid-State Lasers.</a> Adv. Mater. 12, 1655-1668 (2000).</li><li>Samuel, I. D. W., Turnbull, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organic+Semiconductor+Lasers.">Organic Semiconductor Lasers.</a> Chem. Rev. 107, 1272-1295 (2007).</li><li>Kuehne, A. J. C., Gather, M. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organic+Lasers:+Recent+Developments+on+Materials,+Device+Geometries,+and+Fabrication+Techniques.">Organic Lasers: Recent Developments on Materials, Device Geometries, and Fabrication Techniques.</a> Chem. Rev. 116, 12823-12864 (2016).</li><li>Furumi, S., Kanai, T., Sawada, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Widely+Tunable+Lasing+in+a+Colloidal+Crystal+Gel+Film+Permanently+Stabilized+by+an+Ionic+Liquid.">Widely Tunable Lasing in a Colloidal Crystal Gel Film Permanently Stabilized by an Ionic Liquid.</a> Adv. Mater. 23, 3815-3820 (2011).</li><li>Mikosch, A., Ciftci, S., Kuehne, A. J. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Colloidal+Crystal+Lasers+from+Monodisperse+Conjugated+Polymer+Particles+via+Bottom-Up+Coassembly+in+a+Sol-Gel+Matrix.">Colloidal Crystal Lasers from Monodisperse Conjugated Polymer Particles via Bottom-Up Coassembly in a Sol-Gel Matrix.</a> ACS Nano. 10, 10195-10201 (2016).</li><li>Oraevsky, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Whispering-Gallery+Waves.">Whispering-Gallery Waves.</a> Quant Electron. 32 (5), 377-400 (2002).</li><li>Yamamoto, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spherical+Resonators+from+&#960;-Conjugated+Polymers.">Spherical Resonators from &#960;-Conjugated Polymers.</a> Polym. J. 48, 1045-1050 (2016).</li><li>Adachi, T., 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=Spherical+Assemblies+from+&#960;+-Conjugated+Alternating+Copolymers:+Toward+Optoelectronic+Colloidal+Crystals.">Spherical Assemblies from &#960; -Conjugated Alternating Copolymers: Toward Optoelectronic Colloidal Crystals.</a> J. Am. Chem. Soc. 135, 870-876 (2013).</li><li>Tong, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tetramethylbithiophene+in+&#960;-Conjugated+Alternating+Copolymers+as+an+Effective+Structural+Component+for+the+Formation+of+Spherical+Assemblies.">Tetramethylbithiophene in &#960;-Conjugated Alternating Copolymers as an Effective Structural Component for the Formation of Spherical Assemblies.</a> Polym. 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The selection of a good solvent and non-solvent is very important for the self-assembly of well-defined microspheres. If the solubility of a polymer is too high, precipitation will not occur. Also, in general, &#960;-conjugated polymers are hydrophobic, so polar non-solvents, such as MeOH, acetonitrile, and acetone, are often used in the vapor diffusion method to minimize the surface energy required to form a spherical shape. The interface precipitation method is often adopted for the preparation of dye-doped polymer mic...

Polymer nano/micro-sized particles are widely used for a variety of applications, including as catalyst support, column chromatography fillers, drug delivery agents, fluorescent probes for cell tracking, optical media, and so forth1,2,3,4,5,6,7,8,9. In particular, &#960;-conjugated polymers have inherent luminescent and charge conducting properties that are beneficial to optical, electronic, and optoelectronic applications using polymer spheres10,11,12,13,14, especially laser applications using soft organic materials15,16,17. For example, the three-dimensional integration of spheres with several hundred nanometer diameters forms colloidal crystals, which show photonic band gaps at a certain wavelength18,19. When light is confined in the intersphere periodic structure, lasing action appears at the middle of the stop band. On the other hand, when the size of the spheres increases to the several-micrometer scale, light is confined inside a single microsphere via total internal reflection at the polymer/air interface20. Propagation of the light wave at the maximum circumference results in interference, leading to the appearance of a resonant mode with sharp and periodic emission lines. These optical modes are so-called &#34;whispering gallery modes&#34; (WGMs). The term &#34;whispering gallery&#34; originated from St. Paul&#39;s Cathedral in London, where sound waves propagate along the circumference of the wall, allowing whispers to be heard by a person on the other side of the gallery. Because the wavelength of light is on the sub-micrometer scale, which is far smaller than sound waves, such a large dome is not necessary for the WGM of light: tiny, micrometer-scale, well-defined vessels, such as microspheres, microdiscs, and microcrystals, fulfill the WGM conditions.
Equation 1 is a simple form of the WGM resonating condition21:
n&#960;d = l&#955;&#160;&#160;&#160;&#160;&#160; (1)
where n is the refractive index of the resonator, d is the diameter, l is the integer number, and &#955; is the wavelength of the light. The left part of (1) is the optical path length through one circle propagation. When the optical path coincides with the integer multiple of the wavelength, resonance occurs, while at the other wavelength, the light wave is diminished upon rounding.
This paper introduces several experimental methods to prepare microspheres for WGM resonators from conjugated polymers in solution: vapor diffusion22,23,24,25,26,27,28,29,30, mini-emulsion31, and interface precipitation32. Each method has unique characteristics; for example, the vapor diffusion method affords well-defined microspheres with very high sphericity and smooth surfaces, but only low-crystallinity polymers can form these microspheres. On the other hand, for the mini-emulsion method, various kinds of conjugated polymers, including high-crystalline polymers, can form spheres, but the surface morphology is inferior to that obtained from the vapor diffusion method. The interface precipitation method is preferable for creating microspheres from dye-doped, non-conjugated polymers. In all cases, the selection of the solvent and the non-solvent plays an important role in the formation of spherical morphology.
In the second half of this paper, &#181;-PL and micro-manipulation techniques are presented. For the &#181;-PL technique, microspheres are dispersed on a substrate, and a focused laser beam, through a microscope lens, is used to irradiate a single isolated microsphere24. The generated PL from a sphere is detected by a spectrometer through the microscope lens. Moving the sample stage can vary the position of the excitation spot. The detection point is also variable by tilting the collimator optics of the excitation laser beam with respect to the optical axis of the detection path28,32. To investigate intersphere light propagation and wavelength conversion, the micro-manipulation technique can be used32. To connect several microspheres with different optical properties, it is possible to pick up one sphere using a micro-needle and put it on another sphere. In conjunction with the micromanipulation techniques and the &#181;-PL method, various optical measurements can be carried out using conjugated polymer spheres, which are prepared by a simple self-assembly method. This video paper will be useful to readers who wish to use soft polymer materials for optical applications.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>polystyrene</td>
			<td>Aldrich</td>
			<td>132427-25G</td>
			<td></td>
		</tr>
		<tr>
			<td>sodium dodecylsulfate</td>
			<td>Kanto Kagaku</td>
			<td>372035-31</td>
			<td></td>
		</tr>
		<tr>
			<td>tetrahydrofuran</td>
			<td>Wako</td>
			<td>206-08744</td>
			<td></td>
		</tr>
		<tr>
			<td>chloroform</td>
			<td>Wako</td>
			<td>038-18495</td>
			<td></td>
		</tr>
		<tr>
			<td>methanol</td>
			<td>Wako</td>
			<td>139-13995</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(9,9-di-n-octylfluorenyl-2,7-diyl)</td>
			<td>Aldrich</td>
			<td>571652-500MG</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly[2-methoxy-5-(3&#8242;,7&#8242;-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMOPPV)</td>
			<td>Aldrich</td>
			<td>546461-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>poly[(9,9-dioctylfluorene-2,7-diyl)-alt-(5-octylthieno[3,4-c]pyrrole-4,6-dione-1,3-diyl)] (P1)</td>
			<td>synthesized</td>
			<td>-</td>
			<td>reference 28</td>
		</tr>
		<tr>
			<td>poly[(N-(2-heptylundecyl)carbazole-2,7-diyl)-alt-(4,8-bis[(dodecyl)carbonyl]benzo[1,2-b:4,5-b&#8242;]dithiophene-2,6-diyl)] (P2)</td>
			<td>synthesized</td>
			<td>-</td>
			<td>reference 28</td>
		</tr>
		<tr>
			<td>fluorescent dye (boron dipyrrin; BODIPY)</td>
			<td>synthesized</td>
			<td>-</td>
			<td>reference 32</td>
		</tr>
		<tr>
			<td>Optical Microscope</td>
			<td>Nicon</td>
			<td>Eclipse LV-N</td>
			<td></td>
		</tr>
		<tr>
			<td>laser_405 nm</td>
			<td>Hutech</td>
			<td>DH405-10-5</td>
			<td></td>
		</tr>
		<tr>
			<td>laser_355 nm</td>
			<td>CNI</td>
			<td>MPL-F-355-10&#65357;W</td>
			<td></td>
		</tr>
		<tr>
			<td>Spectrometer</td>
			<td>Lambda Vision</td>
			<td>LV-MC3/T</td>
			<td></td>
		</tr>
		<tr>
			<td>Homogenizer</td>
			<td>Microtech Nichion</td>
			<td>Physcotron NS-360D</td>
			<td></td>
		</tr>
		<tr>
			<td>micromanipulation</td>
			<td>Microsupport</td>
			<td>Quick Pro QP-3RH</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Figure 1 shows schematic representations of the vapor diffusion method (a), mini-emulsion method (b), and interface precipitation method (c). For the vapor diffusion method (Figure 1a), a 5 mL vial containing a CHCl3 solution of polymers (0.5 mg mL-1, 2 mL) was placed in a 50 mL vial containing 5 mL of a non-solvent, such as MeOH. The outside vial was capped and then allowed to stand for 3 days at 25 &#176;C...

Watch this Scientific Journal Video about Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications at JoVE.com

Fabrication of Polymer Microspheres for Optical Resonator and Laser Applications

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, ...

The overall goal of this procedure is to produce optical microresonators for laser devices, optical circuits, and chemical and biological optical sensors. This method can help answer key questions in the functional polymer material sphere such as polymer optics, optoelectronics, and electronics. The main advantage of this simple and low energy consumption technique is that it uses functional polymers to fabricate optical resonators which have both optical and electrical properties.Demonstrating the procedure will be Mr.Okada, Mr.Zakarias, and Mr.Oki, graduate students from my laboratory. To begin the vapor diffusion method for this procedure, add five milliliters of methanol to a 50 milliliter vial. Next, dissolve two milligrams of conjugated polymers in two milliliters of chloroform in a five milliliter vial.Carefully place the five milliliter vial inside the 50 milliliter vial. After this, cap the 50 milliliter vial. Incubate at 25 degrees Celsius for three days to precipitate the polymer microspheres.To begin the mini-emulsion method, dissolve five milligrams of conjugated polymers in one milliliter of chloroform. Then, dissolve 30 milligrams of SDS in two milliliters of deionized water. Add 100 microliters of the polymer mixture to the SDS solution.Using an ultra high speed homogenizer, stir for two minutes at 30, 000 RPM. Allow the emulsion to rest for one day without the cap to evaporate the chloroform. The next day, centrifuge the dispersion in a 1.5 milliliter centrifuge tube for five minutes at 2, 200 times g.After removing the supernatant, add one milliliter of deionized water and shake vigorously. Repeat the centrifugation, supernatant removal, and water wash three times to completely remove any residual SDS. To begin the interface precipitation method, dissolve 20 milligrams of polystyrene in one milligram of fluorescent dye in 20 milliliters of tetrahydrofuran.Add one milliliter of deionized water to an empty 1.5 milliliter microtube. Then, gently pour 0.2 milliliters of the THF solution onto the water layer, being careful to keep the layers from mixing together. Allow the vial to rest for six hours without the cap to precipitate the polymer microspheres.To begin, dilute a suspension of prepared microspheres by 10 times with a poor solvent such methanol or deionized water. Using a spin coater, spin cast one drop of the diluted suspension onto a quartz substrate. Air dry the resulting casted film until the solvents have evaporated completely.Then, transfer the quartz substrate to the sample stage of an optical microscope. Identify an isolated and well-defined microsphere for micro-photoluminescence measurement. Set the laser conditions as outlined in the text protocol and use a focused laser beam to irradiate the microsphere.Using a spectrometer, record the photoluminescence spectrum. Next, take a fluorescent image of the irradiated microsphere. To begin, place the quartz substrate onto the sample stage of an optical microscope.Identify a single well-define microsphere. Then, set a tungsten microneedle on a micromanipulation apparatus. Using a touch panel controller, move the microneedle and pick up the microsphere.Connect the collected microsphere to another single well-defined microsphere. After this, irradiate the microsphere with a focused laser beam. Use a spectrometer to record the photoluminescence spectrum.Then, take a fluorescent image of the irradiated microspheres. In this study, well-defined polymer microspheres are fabricated using three different methods. The vapor diffusion method, the mini-emulsion method, and the interface precipitation method.Scanning electron microscopy shows that the vapor diffusion and interface precipitation methods produce microspheres with very smooth surface morphology. However, those obtained from the mini-emulsion method are rough because the surfactant covers the whole surface. The whispering gallery mode's photoluminescence is then recorded for a single microsphere of polymer one, polymer two, and their blend.The Q factor was seen to reach as 2, 200 for polymer one. Microspheres composed of polymer two however only reached as high as 300, possibly because of their rough surface morphology. Microspheres composed of the polymer blend maintained a high Q factor of 1, 500 likely because of its smooth morphology.Polymorphic polaron dye-doped polystyrene microspheres with photoluminescent colors of green, yellow, orange, and red were connected forming tetraspheres to investigate the intersphere energy transfer cascade. The light energy transfer from green to yellow and from yellow to orange is seen to be efficient while the energy transfer from orange to red did not occur because of the small overlap between the photoluminescent band of the energy donor and the adsorption band of the energy acceptor. Therefore, upconverted energy transfers such as from red to orange, yellow, and green hardly occur.While attempting this procedure, it is important to remember to avoid shaking the vials which may cause a rapid precipitation leading to ill-defined aggregates. Following this procedure, other method like emulsion polymerization and dispersion polymerization methods can be performed in order to answer additional questions like how to prepare monodisperse polymer spheres for application to colloidal photonic crystals. After its development, this technique paved the way for researchers in the field of polymer science to explore optical and laser applications using functional polymers.After watching this video, you should have a good understanding of how to prepare microoptical resonators by bottom up self-assembly process. Don't forget that working with laser devices have to take special care to protect from laser beams that harms your eyes.

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Research

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Engineering

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

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

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

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

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed polymer optical fiber is composed of 80,000 strands of poly (methyl methacrylate) (PMMA) and polystyrene (PS) that are randomly mixed and drawn into a square cross section optical fiber with a side width of 250 &mu;m. Initially, each strand is 200 &mu;m in diameter and 8-inches long. During the mixing process of the original fiber strands, the fibers cross over each other; however, a large draw ratio guarantees that the refractive index profile is invariant along the length of the fiber for several tens of centimeters. The large refractive index difference of 0.1 between the disordered sites results in a small localized beam radius that is comparable to the beam radius of conventional optical fibers. The input light is launched from a standard single mode optical fiber using the butt-coupling method and the near-field output beam from the disordered fiber is imaged using a 40X objective and a CCD camera. The output beam diameter agrees well with the expected results from the numerical simulations. The disordered optical fiber presented in this work is the first device-level implementation of 2D Anderson localization, and can potentially be used for image transport and short-haul optical communication systems.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. This microstructured fiber can transport a small localized beam with a radius that is comparable to the beam radius of conventional optical fibers.

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

Patterning via Optical Saturable Transitions - Fabrication and Characterization

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical Saturable Transitions (POST). In this technique the chemical properties of organic photochromic molecules that undergo single-photon reactions are exploited, enabling rapid top-down nanopatterning over large areas at low light intensities, thereby, allowing for the circumvention of the far-field diffraction barrier.4 Simple, cost-effective, high throughput and resolution alternatives to nanopatterning are being explored, such as, two-photon polymerization5,6, beam pen lithography (BPL)7, scanning electron beam lithography (SEBL), and focused ion beam (FIB) patterning. However, multi-photon approaches require high light intensities, which limit their potential for high throughput and offer low image contrast. Although, electron and ion beam lithographic processes offer increased resolution, the serial nature of the process is limited to slow writing speeds, which also prevents patterning of features over large areas. Beam-pen lithography is an approach towards parallel near-field optical lithography. However, the gap between the source of the beam and the surface of the photoresist needs to be controlled extremely precisely for good pattern uniformity and this is very challenging to accomplish for large arrays of beams. Patterning via Optical Saturable Transitions (POST) is an alternative optical nanopatterning technique for patterning sub-wavelength features1-3. Since this technique uses single photons instead of electrons, it is extremely fast and does not require high light intensities1-3, opening the door to massive parallelization.

We report that the diffraction limit of conventional optical lithography can be overcome by exploiting the transitions of organic photochromic derivatives induced by their photoisomerization at low light intensities.1-3 This paper outlines our fabrication technique and two locking mechanisms, namely: dissolution of one photoisomer and electrochemical oxidation.

This protocol describes the fabrication and characterization of nanostructures using a novel nanolithographic technique called Patterning via Optical ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

Compact Lens-less Digital Holographic Microscope for MEMS Inspection and Characterization

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and automotive. However, effective inspection and characterization metrology systems are needed to ensure the functional reliability of MEMS. This study presents a system based on digital holography as a tool for MEMS metrology. Digital holography has gained increasing attention in the past 20 years. With the fast development and decreasing cost of sensor arrays, resolution of such systems has increased broadening potential applications. Thus, it has attracted attention from both research and industry sides as a potential reliable tool for industrial metrology. Indeed, by recording the interference pattern between an object beam (which contains sample height information) and a reference beam on a CCD camera, one can retrieve the quantitative phase information of an object. However, most of digital holographic systems are bulky and thus not easy to implement on industry production lines. The novelty of the system presented is that it is lens-less and thus very compact. In this study, it is shown that the Compact Digital Holographic Microscope (CDHM) can be used to evaluate several characteristics typically consider as criteria in MEMS inspections. The surface profiles of MEMS in both static and dynamic conditions are presented. Comparison with AFM is investigated to validate the accuracy of the CDHM.

We present a compact reflection digital holographic system (CDHM) for inspection and characterization of MEMS devices. A lens-less design using a diverging input wave providing natural geometrical magnification is demonstrated. Both static and dynamic studies are presented.

A micro-electro-mechanical-system (MEMS) is a widely used component in many industries, including energy, biotechnology, medical, communications, and ...

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

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

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

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

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

Fabrication of 1-D Photonic Crystal Cavity on a Nanofiber Using Femtosecond Laser-induced Ablation

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using femtosecond laser-induced ablation. We show that thousands of periodic nano-craters are fabricated on an optical nanofiber by irradiating with just a single femtosecond laser pulse. For a typical sample, periodic nano-craters with a period of 350 nm and with diameter gradually varying from 50 - 250 nm over a length of 1 mm are fabricated on a nanofiber with diameter around 450 - 550 nm. A key aspect of such a nanofabrication is that the nanofiber itself acts as a cylindrical lens and focuses the femtosecond laser beam on its shadow surface. Moreover, the single-shot fabrication makes it immune to mechanical instabilities and other fabrication imperfections. Such periodic nano-craters on nanofiber, act as a 1-D PhC and enable strong and broadband reflection while maintaining the high transmission out of the stopband. We also present a method to control the profile of the nano-crater array to fabricate apodized and defect-induced PhC cavities on the nanofiber. The strong confinement of the field, both transverse and longitudinal, in the nanofiber-based PhC cavities and the efficient integration to the fiber networks, may open new possibilities for nanophotonic applications and quantum information science.

We present a protocol for fabricating 1-D photonic crystal cavities on subwavelength diameter silica fibers (optical nanofibers) using femtosecond laser-induced ablation.

We present a protocol for fabricating 1-D Photonic Crystal (PhC) cavities on subwavelength-diameter tapered optical fibers, optical nanofibers, using ...

Fabrication of Superhydrophobic Metal Surfaces for Anti-Icing Applications

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

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

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

Fused Filament Fabrication (FFF) of Metal-Ceramic Components

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with diverse customization options and favorable production methods is increasing continuously. With fused filament fabrication (FFF), it is possible to produce large and complex components quickly with high material efficiency. In FFF, a continuous thermoplastic filament is melted in a heated nozzle and deposited below. The computer-controlled print head is moved in order to build up the desired shape layer by layer. Investigations regarding printing of metals or ceramics are increasing more and more in research and industry. This study focuses on additive manufacturing (AM) with a multi-material approach to combine a metal (stainless steel) with a technical ceramic (zirconia: ZrO2). Combining these materials offers a broad variety of applications due to their different electrical and mechanical properties. The paper shows the main issues in preparation of the material and feedstock, device development, and printing of these composites.

Fused Filament Fabrication FFF of Metal-Ceramic Components

This study shows multi-material additive manufacturing (AM) using fused filament fabrication (FFF) of stainless steel and zirconia.

Technical ceramics are widely used for industrial and research applications, as well as for consumer goods. Today, the demand for complex geometries with ...

Design and Fabrication of an Optical Fiber Made of Water

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with solid-cladding devices, capillary oscillations are not restricted, allowing the fiber walls to move and vibrate. The fiber is constructed by a high direct current (DC) voltage of several thousand volts (kV) between two water reservoirs that creates a floating water thread, known as a water bridge. Through the choice of micropipettes, it is possible to control the maximal diameter and length of the fiber. Optical fiber couplers, at both sides of the bridge, activate it as an optical waveguide, allowing researchers to monitor the water fiber capillary body waves through transmission modulation and, therefore, deducing changes in surface tension.
Co-confining two important wave types, capillary and electromagnetic, opens a new path of research in the interactions between light and liquid-wall devices. Water-walled microdevices are a million times softer than their solid counterparts, accordingly improving the response to minute forces.

This protocol describes the design and manufacture of a water bridge and its activation as a water fiber. The experiment demonstrates that capillary resonances of the water fiber modulate its optical transmission.

In this report, an optical fiber of which the core is made solely of water, while the cladding is air, is designed and manufactured. In contrast with ...