Name: phase diagram characterization using magnetic beads as liquid carriers
Uploaded: 2015-09-04T13:00:00
Description: Watch this Scientific Journal Video about Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers at JoVE.com

The authors acknowledge many useful discussions with M. Caggioni and support from Proctor and Gamble in the form of an internship for NAB.

1. Preparation of One-Time Use Materials in Device
<ol>
	<li>Preparation of tube
	<ol>
		<li>Cut tubing into 15 cm segments. Tubing has 1.6 mm inner diameter and 3.2 mm outer diameter.</li>
		<li>Hang tube segments vertically using tape. Place paper towel underneath tubes to collect the excess fluoropolymer solution.</li>
		<li>Inject 100 &#181;l&#160;of fluoropolymer solution into top opening of each tube segment using syringe, such that it will come into contact with entire circumference on the inner-wall.</li>
		<li...

<ol>
	<li>Gijs, M. A., Lacharme, F., Lehmann, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+applications+of+magnetic+particles+for+biological+analysis+and+catalysis.">Microfluidic applications of magnetic particles for biological analysis and catalysis.</a> Chemical review. 110, 1518-1563 (2009).</li><li>Kozissnik, B., Dobson, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomedical+applications+of+mesoscale+magnetic+particles.">Biomedical applications of mesoscale magnetic particles.</a> MRS Bulleti. 38, 927-932 (2013).</li><li>Ali-Cherif, A., Begolo, S., Descroix, S., Viovy, J. -. L., Malaquin, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Programmable+Magnetic+Tweezers+and+Droplet+Microfluidic+Device+for+High-Throughput+Nanoliter+Multi-Step+Assays.">Programmable Magnetic Tweezers and Droplet Microfluidic Device for High-Throughput Nanoliter Multi-Step Assays.</a> Angewandte Chemie International Editio. 51, 10765-10769 (2012).</li><li>Blumenschein, N. A., Han, D., Caggioni, M., Steckl, 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=Magnetic+Particles+as+Liquid+Carriers+in+the+Microfluidic+Lab-in-Tube+Approach+To+Detect+Phase+Change.">Magnetic Particles as Liquid Carriers in the Microfluidic Lab-in-Tube Approach To Detect Phase Change.</a> ACS Applied Materials, &amp; Interface. 6, 8066-8072 (2014).</li><li>Bordelon, H., 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=Development+of+a+low-resource+RNA+extraction+cassette+based+on+surface+tension+valves.">Development of a low-resource RNA extraction cassette based on surface tension valves.</a> ACS applied materials. 3, 2161-2168 (2011).</li><li>Adams, N. M., 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=Design+criteria+for+developing+low-resource+magnetic+bead+assays+using+surface+tension+valves.">Design criteria for developing low-resource magnetic bead assays using surface tension valves.</a> Biomicrofluidic. 7, 014104 (2013).</li><li>Hishida, M., Tanaka, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transition+of+the+hydration+state+of+a+surfactant+accompanying+structural+transitions+of+self-assembled+aggregates.">Transition of the hydration state of a surfactant accompanying structural transitions of self-assembled aggregates.</a> Journal of Physics: Condensed Matte. 24, 284113 (2012).</li><li>Strey, R., Schomacker, R., Roux, D., Nallet, F., Olsson, U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dilute+lamellar+and+L3+phases+in+the+binary+water-C12E5+system.">Dilute lamellar and L3 phases in the binary water-C12E5 system.</a> Journal of the Chemical Society, Faraday Transaction. 86, 2253-2261 (1990).</li><li>Chen, B. -. H., 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=Dissolution+Rates+of+Pure+Nonionic+Surfactants.">Dissolution Rates of Pure Nonionic Surfactants.</a> Langmui. 16, 5276-5283 (2000).</li><li>Warren, P. B., Buchanan, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+surfactant+dissolution.">Kinetics of surfactant dissolution.</a> Current Opinion in Colloid, &amp; Interface Scienc. 6, 287-293 (2001).</li><li>Laughlin, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> The Aqueous Phase Behavior of Surfactant. , (1996).</li><li>Laughlin, R. G., 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=Phase+Studies+by+Diffusive+Interfacial+Transport+Using+Near-Infrared+Analysis+for+Water+(DIT-NIR).">Phase Studies by Diffusive Interfacial Transport Using Near-Infrared Analysis for Water (DIT-NIR).</a> The Journal of Physical Chemistry. 104, 7354-7362 (2000).</li><li>Lynch, M. L., Kochvar, K. A., Burns, J. L., Laughlin, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aqueous-Phase+Behavior+and+Cubic+Phase-Containing+Emulsions+in+the+C12E2&#8722;Water+System.">Aqueous-Phase Behavior and Cubic Phase-Containing Emulsions in the C12E2&#8722;Water System.</a> Langmui. 16, 3537-3542 (2000).</li></ol>

In most common techniques for phase diagram investigation, multiple samples with different compositions and ratios need to be prepared and have to reach thermodynamic equilibrium which causes a lengthy process and a significant amount of material. Some challenges can be resolved by DIT (diffusive interfacial transport) method using flat capillary and the infrared analysis method, but none of them can resolve all challenges with low cost investment.
The feasibility of using magnetic beads as li...

Magnetic beads (MBs) on the order of 1 micrometer in diameter have been used1,2 quite often in microfluidic-based applications, particularly for biomedical devices. In these devices, MBs have offered capabilities such as cell and nucleic acid separation, contrast agents, and drug delivery, to name a few. The combination of external (magnetic field) control and droplet-based microfluidics has enabled3 control of immunoassays using small volumes (&#60;100 nl). MBs have also shown promise when used for liquid handling4. This approach uses the MBs to transport biomolecules between liquid segments within a tube separated by an air valve. This method is not as powerful as other more complex lab-on-chip devices seen in the past, but it is much simpler and does offer the capability of handling microliter-sized volumes of liquid. A similar approach has recently been reported5 by Haselton&#8217;s group and applied to biomedical assays.
One of the most important aspect of this device is the liquid segment separation offered by the surface-tension-controlled air valve. Microliter volumes of liquid attached to MBs are transported through this air gap between liquid segments using an externally applied magnetic field. Microparticle MBs (from ~0.4-7 &#181;m in diameter with an average of 1.9 &#181;m) under the effect of the external magnetic field create a micro-porous cluster that traps liquid within. The strength of this liquid entrapment is sufficient to withstand the forces of surface tension when transporting the MBs from one reservoir to the next. Typically, this effect is undesirable, as most approaches only want transport of specific molecules (such as biomarkers) contained within the liquids6. However, as can be seen in our work, this effect can be utilized to become a positive aspect of the device.
We have utilized this &#8216;lab-in-tube&#8217; approach, shown schematically in Figure 1, for analyzing phase diagrams in binary materials systems. The surfactant C12E5 has been chosen as the main focus of characterization, as it is widely used in industrial applications such as pharmaceuticals, food products, cosmetics, etc. In particular, the H2O/C12E5 binary system was investigated because it provides a rich set of phases to explore. We have focused on one specific aspect of this chemical mixture, namely the transitions to liquid crystalline phases under certain concentrations7-9. This transition is readily observed in our device by incorporating polarizers in the optical microscopy studies in order to highlight phase boundaries.
Being able to map phase diagrams is a very important area of study in order to understand the kinetics involved with phase transition10. The ability to precisely determine the interaction of surfactants with solvents and other components is crucial due to their complexity and many distinct phases11. Many other techniques have previously been used to characterize phase change. The conventional approach involves making many samples, each consisting of different concentrations and allowing them to equilibrate, which requires lengthy processing times and high quantity of sample volumes. Then, samples are typically analyzed by optical methods such as diffusive interfacial transport (DIT), which offers high-resolution of such surfactant compositions12,13. Similar to the method we have utilized, the DIT method uses polarized light to image distinct phase boundaries.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>AccuBead</td>
			<td>Bioneer Inc.</td>
			<td>TS-1010-1</td>
			<td>Magnetic beads</td>
		</tr>
		<tr>
			<td>C12E5 Surfactant</td>
			<td>Sigma-Aldrich</td>
			<td>76437</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermo Scientific Nalgene 890</td>
			<td>Fisher Scientific</td>
			<td>14176178</td>
			<td></td>
		</tr>
		<tr>
			<td>Cube Magnet</td>
			<td>Apex Magnets</td>
			<td>M1CU</td>
			<td></td>
		</tr>
		<tr>
			<td>Polarizer Film</td>
			<td>Edmund Optics</td>
			<td>38-493</td>
			<td></td>
		</tr>
		<tr>
			<td>Teflon AF</td>
			<td>Dupont</td>
			<td>400s1-100-1</td>
			<td>Fluoropolymer solution</td>
		</tr>
		<tr>
			<td>Keyacid Red Dye</td>
			<td>Keystone</td>
			<td>601-001-49</td>
			<td>Fluorescent dye</td>
		</tr>
		<tr>
			<td>Luer-Lock</td>
			<td>Cole-Parmer</td>
			<td>T-45502-12</td>
			<td>Female</td>
		</tr>
		<tr>
			<td>Luer-Lock</td>
			<td>Cole-Parmer</td>
			<td>T-45502-56</td>
			<td>Male</td>
		</tr>
		<tr>
			<td>Syringe</td>
			<td>Fisher Scientific</td>
			<td>14-823-435</td>
			<td>3 mL</td>
		</tr>
		<tr>
			<td>Syringe Pump</td>
			<td>Stoelting</td>
			<td>53130</td>
			<td></td>
		</tr>
		<tr>
			<td>Stereo Microscope</td>
			<td>Nikon</td>
			<td>SMZ-2T</td>
			<td></td>
		</tr>
		<tr>
			<td>Inverted Microscope</td>
			<td>Nikon</td>
			<td>Eclipse Ti-U</td>
			<td>The filter cube used had an excitation wavelength range from 540-580 nm and a dichroic mirror at 585 nm, allowing for photoemission ranging from 593-668 nm.</td>
		</tr>
		<tr>
			<td>Balance</td>
			<td>Denver Instruments&#160;</td>
			<td>PI-225D</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope-Mounted Camera</td>
			<td>Motic</td>
			<td>5000</td>
			<td></td>
		</tr>
	</tbody>
</table>

phase diagram characterization using magnetic beads as liquid carriers

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for the purpose of investigating phase change of those liquid segments. The magnetic beads were externally controlled using a magnet, allowing for the beads to bridge the air valve between the adjacent liquid segments. A hydrophobic coating was applied to the inner surface of the tube to enhance the separation between two liquid segments. The applied magnetic field formed an aggregate cluster of magnetic beads, capturing a certain liquid amount within the cluster that is referred to as carry-over volume. A fluorescent dye was added to one liquid segment, followed by a series of liquid transfers, which then changed the fluorescence intensity in the neighboring liquid segment. Based on the numerical analysis of the measured fluorescence intensity change, the carry-over volume per mass of magnetic beads has been found to be ~2 to 3 &#181;l/mg. This small amount of liquid allowed for the use of comparatively small liquid segments of a couple hundred microliters, enhancing the feasibility of the device for a lab-in-tube approach. This technique of applying small compositional variation in a liquid volume was applied to analyzing the binary phase diagram between water and the surfactant C12E5 (pentaethylene glycol monododecyl ether), leading to quicker analysis with smaller sample volumes than conventional methods.

Using the Lab-in-Tube approach for transporting &#181;l-volume amounts of liquid with magnetic beads along with MATLAB for numerical analysis, average liquid carry-over volumes, as a function of magnetic bead mass, were found (Figure 2). Higher mass of magnetic beads provides higher carry-over volume in the rate of 2-3 &#181;l/mg. The experimental setup (Figure 1) was used to observe phase change within the H2O/C12E5 binary system. Since the H2O/C12E5 system is well...

Watch this Scientific Journal Video about Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers at JoVE.com

Phase Diagram Characterization Using Magnetic Beads as Liquid Carriers

Here, we present a protocol to investigate multi-component phase diagrams using externally controlled magnetic beads as liquid carriers in a lab-in-tube approach. This approach can aid in applications that seek to gather further information on phase change in complex liquid systems.

Magnetic beads with ~1.9 &#181;m average diameter were used to transport microliter volumes of liquids between contiguous liquid segments with a tube for ...

phase-diagram-characterization-using-magnetic-beads-as-liquid-carriers

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Revealing Dynamic Processes of Materials in Liquids Using Liquid Cell Transmission Electron Microscopy

The recent development for in situ transmission electron microscopy, which allows imaging through liquids with high spatial resolution, has attracted significant interests across the research fields of materials science, physics, chemistry and biology. The key enabling technology is a liquid cell. We fabricate liquid cells with thin viewing windows through a sequential microfabrication process, including silicon nitride membrane deposition, photolithographic patterning, wafer etching, cell bonding, etc. A liquid cell with the dimensions of a regular TEM grid can fit in any standard TEM sample holder. About 100 nanoliters reaction solution is loaded into the reservoirs and about 30 picoliters liquid is drawn into the viewing windows by capillary force. Subsequently, the cell is sealed and loaded into a microscope for in situ imaging. Inside the TEM, the electron beam goes through the thin liquid layer sandwiched between two silicon nitride membranes. Dynamic processes of nanoparticles in liquids, such as nucleation and growth of nanocrystals, diffusion and assembly of nanoparticles, etc., have been imaged in real time with sub-nanometer resolution. We have also applied this method to other research areas, e.g., imaging proteins in water. Liquid cell TEM is poised to play a major role in revealing dynamic processes of materials in their working environments. It may also bring high impact in the study of biological processes in their native environment.

We have developed a self-contained liquid cell, which allows imaging through liquids using a transmission electron microscope. Dynamic processes of nanoparticles in liquids can be revealed in real time with sub-nanometer resolution.

The recent development for in situ transmission electron microscopy, which allows imaging through liquids with high spatial resolution, has attracted ...

Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via stereotactic radiotherapy where positioning accuracy allows delivering very high doses per fraction in a small volume of the patient. Dosimetric measurements on medical accelerators are conventionally realized using air-filled ionization chambers. However, in small beams these are subject to nonnegligible perturbation effects. This study focuses on liquid ionization chambers, which offer advantages in terms of spatial resolution and low fluence perturbation. Ion recombination effects are investigated for the microLion detector (PTW) used with the Cyberknife system (Accuray). The method consists of performing a series of water tank measurements at different source-surface distances, and applying corrections to the liquid detector readings based on simultaneous gaseous detector measurements. This approach facilitates isolating the recombination effects arising from the high density of the liquid sensitive medium and obtaining correction factors to apply to the detector readings. The main difficulty resides in achieving a sufficient level of accuracy in the setup to be able to detect small changes in the chamber response.

A growing number of radiation therapy devices offer the advantage of delivering the dose through very small beams to the tumor, allowing for increased conformity and higher doses per fraction. Many different detectors can be used for the dosimetry of these small fields. In the present study, the effect of ion recombination is investigated for a liquid ionization chamber using a stereotactic radiation therapy system.

Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via ...

Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is reported. The measurements were demonstrated at the 1-BM bending magnet beamline of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). By using a 2-D checkerboard &#960;/2 phase-shift grating, transverse coherence lengths were obtained along the vertical and horizontal directions as well as along the 45&#176; and 135&#176; directions to the horizontal direction. Following the technical details specified in this paper, interferograms were measured at different positions downstream of the phase grating along the beam propagation direction. Visibility values of each interferogram were extracted from analyzing harmonic peaks in its Fourier Transformed image. Consequently, the coherence length along each direction can be extracted from the evolution of visibility as a function of the grating-to-detector distance. The simultaneous measurement of coherence lengths in four directions helped identify the elliptical shape of the coherence area of the Gaussian-shaped X-ray source. The reported technique for multiple-direction coherence characterization is important for selecting the appropriate sample size and orientation as well as for correcting the partial coherence effects in coherence scattering experiments. This technique can also be applied for assessing coherence preserving capabilities of X-ray optics.

The measurement protocol and data analysis procedure are given for obtaining transverse coherence of a synchrotron radiation X-ray source along four directions simultaneously using a single 2-D checkerboard phase grating. This simple technique can be applied for complete transverse coherence characterization of X-ray sources and X-ray optics.

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is ...

Frequency Mixing Magnetic Detection Scanner for Imaging Magnetic Particles in Planar Samples

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. It consists of two magnetic measurement heads on both sides of the sample mounted on the legs of a u-shaped support. The sample is locally exposed to a magnetic excitation field consisting of two distinct frequencies, a stronger component at about 77 kHz and a weaker field at 61 Hz. The nonlinear magnetization characteristics of superparamagnetic particles give rise to the generation of intermodulation products. A selected sum-frequency component of the high and low frequency magnetic field incident on the magnetically nonlinear particles is recorded by a demodulation electronics. In contrast to a conventional MPI scanner, p-FMMD does not require the application of a strong magnetic field to the whole sample because mixing of the two frequencies occurs locally. Thus, the lateral dimensions of the sample are just limited by the scanning range and the supports. However, the sample height determines the spatial resolution. In the current setup it is limited to 2 mm. As examples, we present two 20 mm &#215; 25 mm p-FMMD images acquired from samples with 1 &#181;m diameter maghemite particles in silanol matrix and with 50 nm magnetite particles in aminosilane matrix. The results show that the novel MPI scanner can be applied for analysis of thin biological samples and for medical diagnostic purposes.

A scanner for imaging magnetic particles in planar samples was developed using the planar frequency mixing magnetic detection technique. The magnetic intermodulation product response from the nonlinear nonhysteretic magnetization of the particles is recorded upon a two-frequency excitation. It can be used to take 2D images of thin biological samples.

The setup of a planar Frequency Mixing Magnetic Detection (p-FMMD) scanner for performing Magnetic Particles Imaging (MPI) of flat samples is presented. ...

Studying Dynamic Processes of Nano-sized Objects in Liquid using Scanning Transmission Electron Microscopy

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a microfluidic chamber assembled in the specimen holder for Transmission Electron Microscopy (TEM) and STEM. The microfluidic system consists of two silicon microchips supporting thin Silicon Nitride (SiN) membrane windows. This article describes the basic steps of sample loading and data acquisition. Most important of all is to ensure that the liquid compartment is correctly assembled, thus providing a thin liquid layer and a vacuum seal. This protocol also includes a number of tests necessary to perform during sample loading in order to ensure correct assembly. Once the sample is loaded in the electron microscope, the liquid thickness needs to be measured. Incorrect assembly may result in a too-thick liquid, while a too-thin liquid may indicate the absence of liquid, such as when a bubble is formed. Finally, the protocol explains how images are taken and how dynamic processes can be studied. A sample containing AuNPs is imaged both in pure water and in saline.

This protocol describes the operation of a liquid flow specimen holder for scanning transmission electron microscopy of AuNPs in water, as used for the observation of nanoscale dynamic processes.

Samples fully embedded in liquid can be studied at a nanoscale spatial resolution with Scanning Transmission Electron Microscopy (STEM) using a ...

Characterization of Ultra-fine Grained and Nanocrystalline Materials Using Transmission Kikuchi Diffraction

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and nanocrystalline materials. The traditional techniques associated with scanning electron microscopy (SEM), such as electron backscatter diffraction (EBSD), do not possess the required spatial resolution due to the large interaction volume between the electrons from the beam and the atoms of the material. Transmission electron microscopy (TEM) has the required spatial resolution. However, due to a lack of automation in the analysis system, the rate of data acquisition is slow which limits the area of the specimen that can be characterized. This paper presents a new characterization technique, Transmission Kikuchi Diffraction (TKD), which enables the analysis of the microstructure of UFG and nanocrystalline materials using an SEM equipped with a standard EBSD system. The spatial resolution of this technique can reach 2 nm. This technique can be applied to a large range of materials that would be difficult to analyze using traditional EBSD. After presenting the experimental set up and describing the different steps necessary to realize a TKD analysis, examples of its use on metal alloys and minerals are shown to illustrate the resolution of the technique and its flexibility in term of material to be characterized.

This paper provides a detailed method to characterize the microstructure of ultra-fine grained and nanocrystalline materials using a scanning electron microscope equipped with a standard electron backscatter diffraction system. Metal alloys and minerals presenting refined microstructures are analyzed using this technique, showing the diversity of its possible applications.

One of the challenges in microstructure analysis nowadays resides in the reliable and accurate characterization of ultra-fine grained (UFG) and ...

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape method or individual WS2 nanotubes by dispersing the suspension of WS2 nanotubes. The selected samples have been fabricated into devices by the use of the electron beam lithography and electrolyte is put on the devices. We have characterized the electronic properties of the devices under applying the gate voltage. In the small gate voltage region, ions in the electrolyte are accumulated on the surface of the samples which leads to the large electric potential drop and resultant electrostatic carrier doping at the interface. Ambipolar transfer curve has been observed in this electrostatic doping region. When the gate voltage is further increased, we met another drastic increase of source-drain current which implies that ions are intercalated into layers of WS2 and electrochemical carrier doping is realized. In such electrochemical doping region, superconductivity has been observed. The focused technique provides a powerful strategy for achieving the electric-filed-induced quantum phase transition.

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Here, we present a protocol to control the carrier number in solids by using the electrolyte.

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape ...

Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared on transparent membranes which are very fragile and difficult to manipulate. We present processes for the fabrication of samples with magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for Lorentz transmission electron microscopy and magnetic transmission x-ray microscopy studies. The samples are prepared on silicon nitride membranes and the fabrication consists of a spin coating, UV and electron-beam lithography, the chemical development of the resist, and the evaporation of the magnetic material followed by a lift-off process forming the final magnetic structures. The samples for the Lorentz transmission electron microscopy consist of magnetic nanodiscs prepared in a single lithography step. The samples for the magnetic x-ray transmission microscopy are used for time-resolved magnetization dynamic experiments, and magnetic nanodiscs are placed on a waveguide which is used for the generation of repeatable magnetic field pulses by passing an electric current through the waveguide. The waveguide is created in an extra lithography step.

A protocol for the fabrication of magnetic micro- and nanostructures with spin configurations forming magnetic vortices suitable for transmission electron microscopy (TEM) and magnetic transmission x-ray microscopy (MTXM) studies is presented.

Electron and x-ray magnetic microscopies allow for high-resolution magnetic imaging down to tens of nanometers. However, the samples need to be prepared ...

Measuring Magnetically-Tuned Ferroelectric Polarization in Liquid Crystals

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due to their potential applications for future device technologies such as sensors and storage. However, conventional approaches, which usually utilize materials containing magnetic metal ions (or radicals), have a major problem: only a few materials have been found to show the coupling phenomena at room temperature. Recently, we proposed a new approach to achieve room-temperature magnetoelectrics. In contrast to conventional approaches, our alternative proposal focuses on a completely different material, a &#34;liquid crystal&#34;, free from magnetic metal ions. In such liquid crystals, a magnetic field can be utilized to control the orientational state of constituent molecules and the corresponding electric polarization through magnetic anisotropy of the molecules; it is an unprecedented mechanism of the magnetoelectric effect. In this context, this paper provides a protocol to measure ferroelectric properties induced by a magnetic field, that is, the direct magnetoelectric effect, in a liquid crystal. With the method detailed here, we successfully detected magnetically-tuned electric polarization in the chiral smectic C phase of a liquid crystal at room temperature. Taken together with the flexibility of constituent molecules, which directly affects the magnetoelectric responses, the introduced method will serve to allow liquid crystal cells to acquire more functions as room-temperature magnetoelectrics and associated optical materials.

In this report, we present a protocol to examine direct magnetoelectric effects, i.e., induction of ferroelectric polarization by applying magnetic fields, in liquid crystals. This protocol provides a unique approach, supported by the softness of liquid crystals, to achieve room-temperature magnetoelectrics.

Materials showing coupling phenomena between magnetism and (ferro)electricity, i.e., magnetoelectric effects, have attracted a great deal of attention due ...

Shaping the Amplitude and Phase of Laser Beams by Using a Phase-only Spatial Light Modulator

The aim of this article is to visually demonstrate the utilization of an interferometric method for encoding complex fields associated with coherent laser radiation. The method is based on the coherent sum of two uniform waves, previously encoded into a phase-only spatial light modulator (SLM) by spatial multiplexing of their phases. Here, the interference process is carried out by spatial filtering of light frequencies at the Fourier plane of certain imaging system. The correct implementation of this method allows arbitrary phase and amplitude information to be retrieved at the output of the optical system.
It is an on-axis, rather than off-axis encoding technique, with a direct processing algorithm (not an iterative loop), and free from coherent noise (speckle). The complex field can be exactly retrieved at the output of the optical system, except for some loss of resolution due to the frequency filtering process. The main limitation of the method might come from the inability to operate at frequency rates higher than the refresh rate of the SLM. Applications include, but are not limited to, linear and non-linear microscopy, beam shaping, or laser micro-processing of material surfaces.

We show how to encode the complex field of laser beams by using a single phase element. A common-path interferometer is employed to mix the phase information displayed into a phase-only spatial light modulator to finally retrieve the desired complex field pattern at the output of an optical imaging system.

The aim of this article is to visually demonstrate the utilization of an interferometric method for encoding complex fields associated with coherent laser ...