Name: large area substrate-based nanofabrication of controllable and customizable gold nanoparticles via capped dewetting
Uploaded: 2019-02-26T14:30:00
Description: Watch this Scientific Journal Video about Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting at JoVE.com

We acknowledge the support from the Microscopy Core Facility at Utah State University for the SEM result. We also acknowledge the National Science Foundation (Award #162344) for the DC Magnetron Sputtering System, the National Science Foundation (Award #133792) for the (Field Electron and Ion) FEI Quanta 650, and the Department of Energy, Nuclear Energy University Program for the FEI Nova Nanolab 600.

NOTE: The large-area fabrication of controllable and customizable gold nanoparticle films is achieved by following the detailed protocol. The protocol follows three major areas that are (1) substrate preparation, (2) dewetting and etching, and (3) characterization.
1. Substrate Preparation
<ol>
	<li>Clean the substrate (100 nm SiO2 on Si) using an acetone rinse followed by an isopropyl alcohol rinse and then dry using a stream of N2 gas.</li>
	<li>Load the substrate int...

<ol>
	<li>Pillai, S., Catchpole, K. R., Trupke, T., Green, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+plasmon+enhanced+silicon+solar+cells.">Surface plasmon enhanced silicon solar cells.</a> Journal of Applied Physics. 101 (9), 093105 (2007).</li><li>Ding, B., Lee, B. J., Yang, M., Jung, H. S., Lee, J. -. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface-Plasmon+Assisted+Energy+Conversion+in+Dye-Sensitized+Solar+Cells.">Surface-Plasmon Assisted Energy Conversion in Dye-Sensitized Solar Cells.</a> Advanced Energy Materials. 1 (3), 415-421 (2011).</li><li>Tehrani, S., Chen, E., Durlam, M., DeHerrera, M., Slaughter, J. M., Shi, J., Kerszykowski, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+density+submicron+magnetoresistive+random+access+memory+(invited).">High density submicron magnetoresistive random access memory (invited).</a> Journal of Applied Physics. 85 (8), 5822-5827 (1999).</li><li>Ross, C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+patterned+media+for+high+density+magnetic+storage.">Fabrication of patterned media for high density magnetic storage.</a> Journal of Vacuum Science &amp; Technology B. 17, 3168 (1999).</li><li>Gu, M., Zhang, Q., Lamon, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanomaterials+for+optical+data+storage.">Nanomaterials for optical data storage.</a> Nature Reviews Materials. 1, 16070 (2016).</li><li>Mock, J. J., Barbic, M., Smith, D. R., Schultz, D. A., Schultz, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+effects+in+plasmon+resonance+of+individual+colloidal+silver+nanoparticles.">Shape effects in plasmon resonance of individual colloidal silver nanoparticles.</a> The Journal of Chemical Physics. 116 (15), 6755-6759 (2002).</li><li>Su, K. -. H. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Interparticle+Coupling+Effects+on+Plasmon.">Interparticle Coupling Effects on Plasmon.</a> Resonances of Nanogold Particles, Nano Letters. 3 (8), 1087-1090 (2003).</li><li>Lee, K., El-Sayed, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gold+and+Silver+Nanoparticles+in+Sensing+and+Imaging:+Sensitivity+of+Plasmon+Response+to+Size,+Shape,+and+Metal+Composition.">Gold and Silver Nanoparticles in Sensing and Imaging: Sensitivity of Plasmon Response to Size, Shape, and Metal Composition.</a> The Journal of Physical Chemistry B. 110 (39), 19220-19225 (2006).</li><li>Grzelczak, M., Prez-Juste, J., Mulvaney, P., Liz-Marzn, L. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+control+in+gold+nanoparticle+synthesis.">Shape control in gold nanoparticle synthesis.</a> Chemical Society Reviews. 37 (9), 1783-1791 (2008).</li><li>Ye, J., Thompson, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Templated+Solid-State+Dewetting+to+Controllably+Produce+Complex+Patterns.">Templated Solid-State Dewetting to Controllably Produce Complex Patterns.</a> Advanced Materials. 23 (13), 1567-1571 (2011).</li><li>Huang, J., Kim, F., Tao, A., Connor, S., Yang, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spontaneous+formation+of+nanoparticle+stripe+patterns+through+dewetting.">Spontaneous formation of nanoparticle stripe patterns through dewetting.</a> Nature Materials. 4, 896-900 (2005).</li><li>Hughes, R. A., Menumerov, E., Neretina, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=When+lithography+meets+self-assembly:+a+review+of+recent+advances+in+the+directed+assembly+of+complex+metal+nanostructures+on+planar+and+textured+surfaces.">When lithography meets self-assembly: a review of recent advances in the directed assembly of complex metal nanostructures on planar and textured surfaces.</a> Nanotechnology. 28 (28), 282002 (2017).</li><li>Kim, D., Giermann, A. L., Thompson, C. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solid-state+dewetting+of+patterned+thin+films.">Solid-state dewetting of patterned thin films.</a> Applied Physics Letters. 95 (25), 251903 (2009).</li><li>Fowlkes, J. D., Doktycz, M. J., Rack, P. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+optimized+nanoparticle+separator+enabled+by+electron+beam+induced+deposition.">An optimized nanoparticle separator enabled by electron beam induced deposition.</a> Nanotechnology. 21 (16), 165303 (2010).</li><li>White, B. C. A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Effect+of+Different+Thickness+Alumina+Capping+Layers+on+the+Final+Morphology+of+Dewet+Thin+Ni+Films.">The Effect of Different Thickness Alumina Capping Layers on the Final Morphology of Dewet Thin Ni Films.</a> Applied Physics A. 124 (3), 233 (2018).</li></ol>

The protocol is a feasible and easy process for a nano-manufacturing process for producing nanoparticles on a substrate over large areas with controllable characteristics. The dewetting phenomenon, which leads to the production of particles, is based on the tendency of the dewetted layer to achieve minimum surface energy. The control over the size and shape of the particles is targeted with the deposition of a second surface on the main layer to tune the surface energies, and the final equilibrium between the adhesion an...

Large-area nanoparticle film fabrication is critically important for the adoption of recent technological advances in solar energy conversion and high-density data storage with the use of plasmonic nanoparticles1,2,3,4,5. Interestingly, it is the magnetic properties of some of these plasmonic nanoparticles, which provide these nanoparticles with the ability to manipulate and control light at the nanoscale. This controllability of light provides the possibility to enhance light entrapment of the incident light at the nanoscale and increase the absorptivity of the surface. Based on these same properties and having the ability to have nanoparticles in either a magnetized and a non-magnetized state, scientists are also defining a new platform for high-density digital data storage. In each of these applications, it is critical that a large area and affordable nanofabrication technique is developed that allows for the control of nanoparticle size, spacing, and shape.
The available techniques to produce nanoparticles are mostly based on nanoscale lithography, which have significant scalability and cost issues. There have been multiple different studies that have attempted to address the scalability problem of these techniques, but to date, no process exists that provides the level of control needed for nanoparticle fabrication and is cost and time effective enough for adoption in industrial applications6,7,8,9,10,11. Some recent research efforts improved the controllability of pulsed laser induced dewetting (PLiD) and templated solid-state dewetting12,13,14, but they still have significant required lithography steps and thus the scalability problem.
In this manuscript, we present the protocol of a nanofabrication method that will address this scalability and cost issue that has plagued the adoption and use of nanoparticle films in widespread industrial applications. This processing method allows the control over the produced nanoparticle size and spacing by manipulating the surface energies which dictate the self-assembly of the nanoparticles formed. Here, we demonstrate the use of this technique using a thin gold film to produce gold nanoparticles, but we have recently published a slightly different version of this method using a nickel film and thus this technique can be used with any desired metal. The goal of this method is to produce nanoparticle films while minimizing the cost and complexity of the process and thus we have modified our previous approach, which used atomic layer deposition and nanosecond laser irradiation on a Ni-alumina system and replaced them with physical vapor deposition and a hot plate. The result of our work on a Ni-alumina system also showed an acceptable level of control on the morphology of the surface after the dewetting15.

<table>
	<tbody>
		<tr>
			<td>100 nm SiO2/Si Substrate</td>
			<td>University Wafer</td>
			<td>Thermal Oxide Wafer</td>
			<td></td>
		</tr>
		<tr>
			<td>Alumina Sputter Target (99.5%)</td>
			<td>Kurt J. Lesker</td>
			<td>Alumina Target</td>
			<td></td>
		</tr>
		<tr>
			<td>Gold Wire (99.99%)</td>
			<td>Kurt J. Lesker</td>
			<td>Gold Wire</td>
			<td></td>
		</tr>
		<tr>
			<td>H2O2</td>
			<td>Sigma-Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hot Plate</td>
			<td>Thermo Scientific</td>
			<td>Cimarec</td>
			<td></td>
		</tr>
		<tr>
			<td>NH4OH</td>
			<td>Sigma-Aldrich</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning Electron Microscope</td>
			<td>FEI</td>
			<td>Quanta 650</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning Electron Microscope</td>
			<td>FEI</td>
			<td>Nova Nanolab 600</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputter Deposition System</td>
			<td>AJA International</td>
			<td>Orion-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermal Evaporator</td>
			<td>Edwards</td>
			<td>360</td>
			<td></td>
		</tr>
	</tbody>
</table>

large area substrate-based nanofabrication of controllable and customizable gold nanoparticles via capped dewetting

Recent scientific advances in the utilization of metallic nanoparticle for enhanced energy conversion efficiency, improved optical device performance, and high-density data storage have demonstrated the potential benefit of their use in industrial applications. These applications require precise control over nanoparticle size, spacing, and sometimes shape. These requirements have resulted in the use of time and cost intensive processing steps to produce nanoparticles, thus making the transition to industrial application unrealistic. This protocol will resolve this issue by providing a scalable and affordable method for the large-area production of nanoparticle films with improved nanoparticle control compared to the current techniques. In this article, the process will be demonstrated with gold, but other metals can also be used.

The protocol described here has been used for multiple metals and has shown the ability to produce nanoparticles on a substrate over large-area, with controllable size and spacing. Figure 1 shows the protocol with representative results showing the ability to control the fabricated nanoparticle size and spacing. When following this protocol, the result, which is the fabricated nanoparticle film with size and spacing distributions, will be dependent upon the c...

Watch this Scientific Journal Video about Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting at JoVE.com

Large Area Substrate-Based Nanofabrication of Controllable and Customizable Gold Nanoparticles Via Capped Dewetting

This protocol details a novel nano-manufacturing technique that can be used to make controllable and customizable nanoparticle films over large areas based on the self-assembly of dewetting of capped metal films.

Recent scientific advances in the utilization of metallic nanoparticle for enhanced energy conversion efficiency, improved optical device performance, and ...

Our protocol provides a technique to customize nanoparticle distribution, fabricated on a substrate, with changing the dewetting dynamics, without changing the material thickness. Our technique is simple, yet still provides a range of particle sizes. Other techniques out there require extensive lithographic steps to provide the particle control.Our control of particle distribution provides a technique for nanoparticle fabrication that benefits research focused on solar energy conversion, creating photonic devices, and increasing density of data storage. Pay close attention to the deposition thicknesses at each step. Our technique is extremely sensitive to layer thicknesses.Seeing the experiment performed provides a level of detail that can't be conveyed in print. Seeing examples moving throughout the process is essential. First, clean a 100 nanometer silicon dioxide on silicon substrate, using an acetone rinse, followed by an isopropyl alcohol rinse.Dry the substrate using a stream of nitrogen gas. Load the substrate into a thermal evaporator system and evacuate the chamber to reach the desired pressure for the deposition of the metal film. Ensure that the chamber is evacuated to a pressure on the order of 10 to the minus six torr for the removal of air and water vapor in the chamber.Using the thermal evaporator system, deposit the gold film at the desired thickness, which is five nanometers in this experiment. At the second deposition stages, the argon pressure is one to five millitorr, and the range is given as different pressures are chosen to calibrate for the deposition rate. Our technique is extremely sensitive to film thicknesses, as shown in our results.It is critical to calibrate the deposition rates prior to depositing the films, to ensure appropriate thicknesses. Following deposition, vent the chamber and remove the substrate, with the deposited metal film, from the thermal evaporator system. Next, load the substrate, with a deposited metal film, into a direct current magnetron sputter deposition system and evacuate to reach the desired pressure for deposition of the capping film.To locate the sample in the system, put the sample in the load lock. And the device transfers the sample to the main deposition chamber to ensure a sufficient level of vacuum. Now, deposit the capping layer of the desired material and thickness, following a similar procedure and condition as the gold layer deposition.With variable thickness Illumina, in this case. Following deposition, vent the chamber and remove the prepared sample from the sputter deposition system. Place the five nanometer gold film, capped with Illumina, onto a pre-heated hot plate at 300 degrees Celsius, and allow the sample to dewet for one hour.Etch the Illumina, while leaving the gold and underlying substrate with an aqueous solution of ammonium hydroxide and hydrogen peroxide at 80 degrees Celsius for one hour. For characterization, prepare the sample to be vacuum-compatible by rinsing with acetone and isopropyl alcohol. Then, dry the sample using a stream of nitrogen gas.Image the nanoparticle films using scanning electron microscopy under high vacuum and at high magnification. Perform image analysis to obtain information on nanoparticle size and spacing distributions. The protocol described here has been used for multiple metals and has shown the ability to produce nanoparticles on a substrate over large area, with controllable size and spacing.Representative results are shown here, and highlight the ability to control the fabricated nanoparticle size and spacing. The size and spacing distributions of the fabricated nanoparticle film will be dependent upon the metal, the substrate, the capping layer material, the metal thickness, and the capping layer thickness. As an example, the five nanometer gold film on silicon dioxide, with aluminum oxide capping layer thickness of zero, five, 10, and 20 nanometers result in an average nanoparticle radii of 14.2, 18.4, 17.3, and 15.6 nanometers respectively.And an average nonoparticle spacing of 36.9, 56.9, 51.3, and 47.2 nanometers respectively. For the desired particle distribution, accurate control of the deposition layer thicknesses is critical. Depending on the application of your nanoparticle films, more characterization may be required.This would include application-based measurements, like light absorption and magnetic properties. Studies of nanoparticle films in application can be performed using this technique, to control their particle size and distribution. Appropriate personal protective equipments should be worn.Especially do not come into contact with the etchings. Avoid contact with the hot plate.

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Research

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Engineering

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Nanofabrication of Gate-defined GaAs/AlGaAs Lateral Quantum Dots

A quantum computer is a computer composed of quantum bits (qubits) that takes advantage of quantum effects, such as superposition of states and entanglement, to solve certain problems exponentially faster than with the best known algorithms on a classical computer. Gate-defined lateral quantum dots on GaAs/AlGaAs are one of many avenues explored for the implementation of a qubit. When properly fabricated, such a device is able to trap a small number of electrons in a certain region of space. The spin states of these electrons can then be used to implement the logical 0 and 1 of the quantum bit. Given the nanometer scale of these quantum dots, cleanroom facilities offering specialized equipment- such as scanning electron microscopes and e-beam evaporators- are required for their fabrication. Great care must be taken throughout the fabrication process to maintain cleanliness of the sample surface and to avoid damaging the fragile gates of the structure. This paper presents the detailed fabrication protocol of gate-defined lateral quantum dots from the wafer to a working device. Characterization methods and representative results are also briefly discussed. Although this paper concentrates on double quantum dots, the fabrication process remains the same for single or triple dots or even arrays of quantum dots. Moreover, the protocol can be adapted to fabricate lateral quantum dots on other substrates, such as Si/SiGe.

This paper presents a detailed fabrication protocol for gate-defined semiconductor lateral quantum dots on gallium arsenide heterostructures. These nanoscale devices are used to trap few electrons for use as quantum bits in quantum information processing or for other mesoscopic experiments such as coherent conductance measurements.

A quantum computer is a computer composed of quantum bits (qubits) that takes advantage of quantum effects, such as superposition of states and ...

Electroactive Polymer Nanoparticles Exhibiting Photothermal Properties

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step process that finishes with Negishi coupling. Negishi coupling is a cross-coupling process in which a chemical precursor is first lithiated, followed by transmetallation with ZnCl2. The resultant organozinc compound can be coupled to a dibrominated aromatic precursor to give the conjugated monomer. Polymer films can be prepared via electropolymerization of the monomer and characterized using cyclic voltammetry and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. Nanoparticles (NPs) are prepared via emulsion polymerization of the monomer using a two-surfactant system to yield an aqueous dispersion of the polymer NPs. The NPs are characterized using dynamic light scattering, electron microscopy, and UV-Vis-NIR-spectroscopy. Cytocompatibility of NPs is investigated using the cell viability assay. Finally, the NP suspensions are irradiated with a NIR laser to determine their effectiveness as potential materials for photothermal therapy (PTT).

A protocol is presented for the synthesis and preparation of nanoparticles consisting of electroactive polymers.

A method for the synthesis of electroactive polymers is demonstrated, starting with the synthesis of extended conjugation monomers using a three-step ...

Capillary-based Centrifugal Microfluidic Device for Size-controllable Formation of Monodisperse Microdroplets

Here, we demonstrate a simple method for the rapid production of size-controllable, monodisperse, W/O microdroplets using a capillary-based centrifugal microfluidic device. W/O microdroplets have recently been used in powerful methods that enable miniaturized chemical experiments. Therefore, developing a versatile method to yield monodisperse W/O microdroplets is needed. We have developed a method for generating monodisperse W/O microdroplets based on a capillary-based centrifugal axisymmetric co-flowing microfluidic device. We succeeded in controlling the size of microdroplets by adjusting the capillary orifice. Our method requires equipment that is easier-to-use than with other microfluidic techniques, requires only a small volume (0.1-1 &#181;l) of sample solution for encapsulation, and enables the production of hundreds of thousands number of W/O microdroplets per second. We expect this method will assist biological studies that require precious biological samples by conserving the volume of the samples for rapid quantitative analysis biochemical and biological studies.

Here, we demonstrate a simple production method for size-controllable, monodisperse, water-in-oil (W/O) microdroplets using a capillary-based centrifugal microfluidic device. This method requires only a small sample volume and enables high-yield production. We expect this method will be useful for rapid biochemical and cellular analyses.

Here, we demonstrate a simple method for the rapid production of size-controllable, monodisperse, W/O microdroplets using a capillary-based centrifugal ...

Strain Sensing Based on Multiscale Composite Materials Reinforced with Graphene Nanoplatelets

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are proposed to create the electrical network in this work: (a) the incorporation of the nanoplatelets into the epoxy matrix and (b) the coating of the glass fabric with a sizing filled with the same nanoplatelets. Both types of multiscale composite materials, with an in-plane electrical conductivity of ~10-3 S/m, showed an exponential growth of the electrical resistance as the strain increases due to distancing between adjacent functionalized graphene nanoplatelets and contact loss between overlying ones. The sensitivity of the materials analyzed during this research, using the described procedures, has been shown to be higher than commercially available strain gauges. The proposed procedures for self-sensing of the structural composite material would facilitate the structural health monitoring of components in difficult to access emplacements such as offshore wind power farms. Although the sensitivity of the multiscale composite materials was considerably higher than the sensitivity of metallic foils used as strain gauges, the value reached with NH2 functionalized graphene nanoplatelets coated fabrics was nearly an order of magnitude superior. This result elucidated their potential to be used as smart fabrics to monitor human movements such as bending of fingers or knees. By using the proposed method, the smart fabric could immediately detect the bending and recover instantly. This fact permits precise monitoring of the time of bending as well as the degree of bending.

The integration of conductive nanoparticles, such as graphene nanoplatelets, into glass fiber composite materials creates an intrinsic electrical network susceptible to strain. Here, different methods to obtain strain sensors based on the addition of graphene nanoplatelets into the epoxy matrix or as a coating on glass fabrics are proposed.

The electrical response of NH2-functionalized graphene nanoplatelets composite materials under strain was studied. Two different manufacturing methods are ...

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Here, we present a protocol for the in situ synthesis of gold nanoparticles (AuNPs) within the interlayer space of layered titanate films without the aggregation of AuNPs. No spectral change was observed even after 4 months. The synthesized material has expected applications in catalysis, photo-catalysis, and the development of cost-effective plasmonic devices.

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs ...

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing in combination with new nanofabrication techniques. A plasmon is a quantum of charge density oscillation that lends nanoscale metals such as gold and silver unique optical properties. In particular, gold and silver nanoparticles exhibit localized surface plasmon resonances-collective charge density oscillations on the surface of the nanoparticle-in the visible spectrum. Here, we focus on the fabrication of periodic arrays of anisotropic plasmonic nanostructures. These half-shell (or nanocup) structures can exhibit additional unique light-bending and polarization-dependent optical properties that simple isotropic nanostructures cannot. Researchers are interested in the fabrication of periodic arrays of nanocups for a wide variety of applications such as low-cost optical devices, surface-enhanced Raman scattering, and tamper indication. We present a scalable technique based on colloidal lithography in which it is possible to easily fabricate large periodic arrays of nanocups using spin-coating and self-assembled commercially available polymeric nanospheres. Electron microscopy and optical spectroscopy from the visible to near-infrared (near-IR) was performed to confirm successful nanocup fabrication. We conclude with a demonstration of the transfer of nanocups to a flexible, conformal adhesive film.

We demonstrate the fabrication of periodic gold nanocup arrays using colloidal lithographic techniques and discuss the importance of nanoplasmonic films.

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing ...

Preparation of Large-area Vertical 2D Crystal Hetero-structures Through the Sulfurization of Transition Metal Films for Device Fabrication

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition metal dichalcogenides (TMDs) MoS2 and WS2 can be prepared on sapphire substrates. By controlling the metal film thicknesses, good layer number controllability, down to a single layer of TMDs, can be obtained using this growth technique. Based on the results obtained from the Mo film sulfurized under the sulfur deficient condition, there are two mechanisms of (a) planar MoS2 growth and (b) Mo oxide segregation observed during the sulfurization procedure. When the background sulfur is sufficient, planar TMD growth is the dominant growth mechanism, which will result in a uniform MoS2 film after the sulfurization procedure. If the background sulfur is deficient, Mo oxide segregation will be the dominant growth mechanism at the initial stage of the sulfurization procedure. In this case, the sample with Mo oxide clusters covered with few-layer MoS2 will be obtained. After sequential Mo deposition/sulfurization and W deposition/sulfurization procedures, vertical WS2/MoS2 hetero-structures are established using this growth technique. Raman peaks corresponding to WS2 and MoS2, respectively, and the identical layer number of the hetero-structure with the summation of individual 2D materials have confirmed the successful establishment of the vertical 2D crystal hetero-structure. After transferring the WS2/MoS2 film onto a SiO2/Si substrate with pre-patterned source/drain electrodes, a bottom-gate transistor is fabricated. Compared with the transistor with only MoS2 channels, the higher drain currents of the device with the WS2/MoS2 hetero-structure have exhibited that with the introduction of 2D crystal hetero-structures, superior device performance can be obtained. The results have revealed the potential of this growth technique for the practical application of 2D crystals.

Through the sulfurization of pre-deposited transition metals, large-area and vertical 2D crystal hetero-structures can be fabricated. The film transferring and device fabrication procedures are also demonstrated in this report.

We have demonstrated that through the sulfurization of transition metal films such as molybdenum (Mo) and tungsten (W), large-area and uniform transition ...

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

Plasmonic gold nanorods can be trapped in liquids and rotated at kHz frequencies using circularly-polarized optical tweezers. Introducing tools for Brownian dynamics analysis and light scatteringspectroscopy leads to a powerful system for research and application in numerous fields of science.

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and ...