This work was supported by JSPS KAKENHI grant Number 16H06037. We sincerely thank Dr. Yuji Sasaki in Hokkaido University for technical assistance for HR-DSC.

1. Preparation of the Liquid Crystal Alignment Layer of a Perfluoropolymer onto Glass Substrates
<ol>
	<li>Preparation of the perfluoropolymer solution
	<ol>
		<li>Prepare 1 mL of the perfluoropolymer solution by dissolving a perfluoropolymer solution (9 wt% polymer) in a commercial solvent at a ratio of 1:2; this ensures uniform films 0.5-1 &#181;m thick to be spin-coated. 
		NOTE: Please see the Materials List for the solution and solvent used.</li>
	</ol>
	</li>
	<li>Coating of the perfluoropolymer onto clean glass substrates
	<ol>
		<li>Wash the glass substrates (typical size: 1 cm x 1 cm) by sonication at 38 or 42 kHz in an alkaline detergent. Repeatedly rinse them with distilled water. Typically, rinse more than 10 times, with 5 min of sonication each time.</li>
		<li>Subject the substrates to UV-O3 cleaner for 10 min.</li>
		<li>Drip 20 &#181;L of the solution from step 1.1 onto the cleaned glass substrates. Immediately spin-coat the solution at 3,500 rpm and room temperature for 70 s. Bake the film at 80 &#176;C for 60 min to remove the solvent and at 200 &#176;C for 60 min for curing.</li>
	</ol>
	</li>
</ol>
2. Preparation of LC Cells
<ol>
	<li>Glue two glass substrates coated with film together using a photo-curable resin and an LED lamp with a wavelength of 365 nm (1.1 W/cm2). Adjust the thickness of the gap between the two substrates to within the range of 2-100 &#181;m by using micrometer-size glass particles or polyethylene naphthalate films.</li>
	<li>Introduce an LC material, 4&#39;-butyl-4-heptyl-bicyclohexyl-4-carbonitrile (CCN47; 0.2-10 &#181;L)9 to the prepared LC cells using a spatula under capillary force at a temperature higher than the isotropic liquid (I)-nematic (N) phase transition temperature. 
	NOTE: CCN47 has a negative dielectric anisotropy, and the phase sequence is Cry 298.6 K SmA 301.3 K N 331.3 K I, where Cry and SmA stand for crystal and smectic A phases. Do not introduce CCN47 in the N phase or SmA phase, because flow-induced alignment would be promoted.</li>
</ol>
3. Sample Characterization
<ol>
	<li>Texture observation by polarizing optical microscopy (POM)10
	<ol>
		<li>Observe the LC cells under POM with 4-100X objective lenses in conjunction with a hot stage to control the sample temperature with &#177; 0.1-K accuracy. Record the textures in more than 5 frames, at even intervals per Kelvin. Use a digital color camera sequentially, both upon cooling and heating in the range of 291-343 K.</li>
	</ol>
	</li>
	<li>Dielectric spectroscopy (DS)11
	<ol>
		<li>Prepare LC cells, with ITO electrodes &#8211; which can have a square or circular shape and can be purchased commercially &#8211; on both substrates. Solder a lead wire to each substrate. 
		NOTE: Please see the Materials List for the substrates used.</li>
		<li>Measure the capacitance or dielectric constant of the LC cells, exactly as used for POM, using a commercial impedance/gain-phase analyzer. Ensure that the state of the samples is equilibrated before each measurement. Measure the time-dependence of capacitance or the dielectric constant of the LC cells by measuring the capacitance of the LC cells manually every 5 min.</li>
		<li>Start the DS measurement only if the capacitance or dielectric constant of the LC cells becomes non-time-dependent.</li>
	</ol>
	</li>
	<li>High-resolution differential scanning calorimetry (HR-DSC)12
	<ol>
		<li>Put the LC cells into a home-made HR-DSC to be examined, exactly as in POM (never use DSC pans). Refer to Reference 12 to design and build an HR-DSC and to learn how to use it. Perform measurements with scan rates of 0.05-0.10 K/min to enhance the minimum temperature resolving power.</li>
	</ol>
	</li>
	<li>Grazing incident X-ray diffraction (GI-XRD)13
	<ol>
		<li>Put either the LC cell (used for POM or DSC) or a sample with a 2 to 5 &#181;L droplet of CCN47 onto a coated substrate on the GI-XRD sample stage, which should be equipped with a temperature controller.</li>
		<li>Equilibrate the sample for more than 10 min at desired temperatures in the range of 291-343 K, both upon cooling and heating.</li>
		<li>Use an incident X-ray beam on the sample, with a minute incident angle around 0.05-0.10&#176;, to extract surface information on molecular orientation and orderings/structures. Swing the incident angle of the X-ray beam to find the optimal incident angle at which the strength of the diffraction is the strongest. Take the measurements at the optimal incident angle. 
		NOTE: Keep in mind that GI-XRD makes it possible to probe interfacial peculiarities on the nanometer scale, thus maximizing the signal from thin layers while minimizing the signal from the bulk. Note that normal XRD geometries, other than GI-XRD, are not surface-sensitive methods, since the X-ray radiation beam has a large penetration depth into materials.</li>
	</ol>
	</li>
</ol>

<ol>
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S., Yokoyama, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+Anchoring+Transition+in+Liquid+Crystals.">Continuous Anchoring Transition in Liquid Crystals.</a> Nature. 362, 525-527 (1993).</li><li>Senyuk, B., 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=Surface+alignment,+anchoring+transitions,+optical+properties,+and+topological+defects+in+the+nematic+phase+of+thermotropic+bent-core+liquid+crystal+A131.">Surface alignment, anchoring transitions, optical properties, and topological defects in the nematic phase of thermotropic bent-core liquid crystal A131.</a> Phys Rev E. 82 (4 Pt 1), 041711 (2010).</li><li>Bechhoefer, J., 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=Critical+Behavior+in+Anchoring+Transitions+of+Nematic+Liquid+Crystals.">Critical Behavior in Anchoring Transitions of Nematic Liquid Crystals.</a> Phys. Rev. Lett. 64 (16), 1911-1914 (1990).</li><li>Dhara, S., 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=Anchoring+Transitions+of+Transversely+Polar+Liquid-Crystal+Molecules+on+Perfluoropolymer+Surfaces.">Anchoring Transitions of Transversely Polar Liquid-Crystal Molecules on Perfluoropolymer Surfaces.</a> Phys. Rev. E. 79 (6 Pt 1), 60701 (2009).</li><li>Aya, S., 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=Stepwise+heat-capacity+change+at+an+orientation+transition+in+liquid+crystals.">Stepwise heat-capacity change at an orientation transition in liquid crystals.</a> Phys. Rev. E. 86 (2), 022512 (2014).</li><li>Aya, S., 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=Thermodynamically+Anchoring-Frustrated+Surface+to+Trigger+Bulk+Discontinuous+Orientational+Transition.">Thermodynamically Anchoring-Frustrated Surface to Trigger Bulk Discontinuous Orientational Transition.</a> Langmuir. 32 (41), 10545-10550 (2016).</li><li>Dhara, S., Madhusudana, N. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physical+characterisation+of+4'-butyl-4-heptyl-bicyclohexyl-4-carbonitrile.">Physical characterisation of 4'-butyl-4-heptyl-bicyclohexyl-4-carbonitrile.</a> Phase Trans. 81 (6), 561-569 (2008).</li><li>Dierking, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Textures of Liquid Crystals. , (2003).</li><li>Perkowski, P., 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=Technical+aspects+of+dielectric+spectroscopy+measurements+of+liquid+crystals.">Technical aspects of dielectric spectroscopy measurements of liquid crystals.</a> Opto-Electronics Review. 16 (3), 271-276 (2008).</li><li>Inaba, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nano-watt+stabilized+DSC+and+ITS+applications.">Nano-watt stabilized DSC and ITS applications.</a> J Therm Anal Calorim. 79 (3), 605-613 (2005).</li><li>Leveiller, F., Boehm, C., Jacquemain, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two-dimensional+crystal+structure+of+cadmium+arachidate+studied+by+synchrotron+X-ray+diffraction+and+reflectivity.">Two-dimensional crystal structure of cadmium arachidate studied by synchrotron X-ray diffraction and reflectivity.</a> Langmuir. 10 (3), 819-829 (1994).</li><li>de Gennes, P. G., Prost, J. <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 Physics of Liquid Crystals (Second Edition). , (1993).</li><li>Aya, S., 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=Critical+Behavior+in+an+Electric-Field-Induced+Anchoring+Transition+in+a+Liquid+Crystal.">Critical Behavior in an Electric-Field-Induced Anchoring Transition in a Liquid Crystal.</a> Phys. Rev. E. 86 (1 Pt 1), 10701 (2012).</li><li>Avrami, 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+Phase+Change.+I+General+Theory.">Kinetics of Phase Change. I General Theory.</a> J. Chem. 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The authors have nothing to disclose.

The 10x POM images taken using a 5-&#181;m LC cell (Figures 1a and b) clearly show that the orientational state of the bulk LC molecules transits between the P and the V orientations upon temperature variation in a first-order manner. This is marked by the domain nucleation and growth processes, with a new orientation differing from the initial orientation by 90&#176;. The transition temperatures upon cooling and heating are 321.5 K and 325.3 K, respectively. Since CCN47 has a birefringe...

In recent years, there has been growing interest in learning how dynamic molecular features and structures of surface molecules in response to external stimuli might affect the bulk orientation of materials in LC states. One example is to use LC biosensors as a new application of LCs1,2. To quantify how many target bio-species are detected, it is important to know how the interfacial LCs that contact adhering target molecules change and evolve, while also detecting and how they transfer/translate their properties into the bulk.
Using models to pursue these answers, we started with systems that have their surface molecular orientation and short-range orderings varying thermodynamically. These systems allow us to correlate the changes in surface orientation and orderings with the resulting bulk orientation in a systematic way. Recently, we found several LC systems that exhibit orientational transitions, where a spontaneous bulk molecular orientation changes with temperature. In principle, orientational transitions can be categorized into either quasi-second-order3,4 or quasi-first-order transition5,6,7,8. The former is accompanied by a continuous bulk molecular reorientation upon changes in temperature, whereas the latter demonstrates a discontinuous one. In this article, we describe an orientational transition in the quasi-first-order manner between the P and the V orientational states. It proceeds in the single nematic (N) phase by changing the temperature. Details will be provided in the Representative Results and the Discussion.
Since orientational change in the bulk should be governed by a change in the surface molecular orientation and short-range orderings, it is apparent that this system can potentially offer insights into how the thermodynamic variation in surface molecular orientation and short-range orderings affects the bulk orientation. In this article, with the goal of understanding the abovementioned issues, we tackled three problems using four complementary methods (i.e., POM, DS, HR-DSC, and GI-XRD): (1) What does the orientational transition look like? (2) Is the orientational transition thermally detectable? (3) Why and how does the orientational transition occur?

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>CYTOP</td>
			<td>Asahi Glass Co. Ltd.</td>
			<td>CTX-809A</td>
			<td></td>
		</tr>
		<tr>
			<td>Solvent for CYTOP</td>
			<td>Asahi Glass Co. Ltd.</td>
			<td>CT-180 Sol.</td>
			<td></td>
		</tr>
		<tr>
			<td>Alkaline detergent</td>
			<td>Merck KGaA</td>
			<td>Extran MA01</td>
			<td></td>
		</tr>
		<tr>
			<td>NOA61</td>
			<td>Norland Products, Inc.</td>
			<td>#37-322</td>
			<td>Purchasable from Edmund Optics</td>
		</tr>
		<tr>
			<td>AL1254</td>
			<td>JSR Corporation</td>
			<td></td>
			<td>Planar alignment material in self-made cells</td>
		</tr>
		<tr>
			<td>4&#8217;-butyl-4-heptyl-bicyclohexyl-4-carbonitrile</td>
			<td>Nematel GmbH &#38; Co. KG</td>
			<td></td>
			<td>Custom-made</td>
		</tr>
		<tr>
			<td>UV-O3 cleaner</td>
			<td>Technovision Inc.</td>
			<td>UV-208</td>
			<td></td>
		</tr>
		<tr>
			<td>Hot-stage system</td>
			<td>Mettler Toledo</td>
			<td>HS82</td>
			<td></td>
		</tr>
		<tr>
			<td>High-Definition Color Camera Head</td>
			<td>Nikon</td>
			<td>DS-Fi1</td>
			<td></td>
		</tr>
		<tr>
			<td>Impedance/gain-phase analyzer</td>
			<td>Solartron Analytical</td>
			<td>1260</td>
			<td></td>
		</tr>
		<tr>
			<td>Indium Tin Oxide (ITO)-coated substrate</td>
			<td>GEOMATEC Co. Ltd.</td>
			<td></td>
			<td>Custom-made</td>
		</tr>
	</tbody>
</table>

orientational transition in a liquid crystal triggered by the thermodynamic growth of interfacial wetting sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

POM images, DS data, HR-DSC data, and GI-XRD patterns were collected during temperature variation, especially in the vicinity of the orientational transition upon both cooling and heating.
Figure 1 represents the evolution of the texture made by POM and DS measurements during the POM observation of the orientational transition from the P (V) to the V (P) orientational state during cooling (heating)....

Watch this Scientific Journal Video about Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets at JoVE.com

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

orientational-transition-liquid-crystal-triggered-thermodynamic

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7.1K Views.  RIKEN Center for Emergent Matter Science (CEMS). Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

Video: Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

Sputter Growth and Characterization of Metamagnetic B2-ordered FeRh Epilayers

Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using sputtering techniques. Here we describe a method for preparing epitaxial thin films of B2-ordered FeRh by sputter deposition onto single crystal MgO substrates. Deposition at a slow rate onto a heated substrate allows time for the adatoms to both settle into a lattice with a well-defined epitaxial relationship with the substrate and also to find their proper places in the Fe and Rh sublattices of the B2 structure. The structure is conveniently characterized with X-ray reflectometry and diffraction and can be visualised directly using transmission electron micrograph cross-sections. B2-ordered FeRh exhibits an unusual metamagnetic phase transition: the ground state is antiferromagnetic but the alloy transforms into a ferromagnet on heating with a typical transition temperature of about 380 K. This is accompanied by a 1% volume expansion of the unit cell: isotropic in bulk, but laterally clamped in an epilayer. The presence of the antiferromagnetic ground state and the associated first order phase transition is very sensitive to the correct equiatomic stoichiometry and proper B2 ordering, and so is a convenient means to demonstrate the quality of the layers that can be deposited with this approach. We also give some examples of the various techniques by which the change in phase can be detected.

A method to prepare epitaxial layers of ordered alloys by sputtering is described. The B2-ordered FeRh compound is used as an example, as it displays a metamagnetic transition that depends sensitively on the degree of chemical order and the exact composition of the alloy.

Chemically ordered alloys are useful in a variety of magnetic nanotechnologies. They are most conveniently prepared at an industrial scale using ...

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 ...

Ultrasound Velocity Measurement in a Liquid Metal Electrode

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently more difficult than measuring the flow of a transparent fluid, since optical methods are not applicable. Ultrasound can be used to measure the velocity of an opaque fluid, not only at isolated points, but at hundreds or thousands of points arrayed along lines, with good temporal resolution. When applied to a liquid metal electrode, ultrasound velocimetry involves additional challenges: high temperature, chemical activity, and electrical conductivity. Here we describe the experimental apparatus and methods that overcome these challenges and allow the measurement of flow in a liquid metal electrode, as it conducts current, at operating temperature. Temperature is regulated within &#177;2 &#176;C using a Proportional-Integral-Derivative (PID) controller that powers a custom-built furnace. Chemical activity is managed by choosing vessel materials carefully and enclosing the experimental setup in an argon-filled glovebox. Finally, unintended electrical paths are carefully prevented. An automated system logs control settings and experimental measurements, using hardware trigger signals to synchronize devices. This apparatus and these methods can produce measurements that are impossible with other techniques, and allow optimization and control of electrochemical technologies like liquid metal batteries.

Ultrasound velocimetry is used to study mixing by fluid flow in liquid metal electrodes. The focus of this manuscript is to illustrate the methods used for making precise, spatially-resolved ultrasound measurements while limiting oxidation and controlling and monitoring temperature, applied current, and the heater power being supplied.

A growing number of electrochemical technologies depend on fluid flow, and often that fluid is opaque. Measuring the flow of an opaque fluid is inherently ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

How to Ignite an Atmospheric Pressure Microwave Plasma Torch without Any Additional Igniters

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a stable and continuous operation of the plasma is possible and the plasma torch can be used for many different applications. On one hand, the hot (3,600 K gas temperature) plasma can be used for chemical processes and on the other hand the cold afterglow (temperatures down to almost RT) can be applied for surface processes. For example chemical syntheses are interesting volume processes. Here the microwave plasma torch can be used for the decomposition of waste gases which are harmful and contribute to the global warming but are needed as etching gases in growing industry sectors like the semiconductor branch. Another application is the dissociation of CO2. Surplus electrical energy from renewable energy sources can be used to dissociate CO2 to CO and O2. The CO can be further processed to gaseous or liquid higher hydrocarbons thereby providing chemical storage of the energy, synthetic fuels or platform chemicals for the chemical industry. Applications of the afterglow of the plasma torch are the treatment of surfaces to increase the adhesion of lacquer, glue or paint, and the sterilization or decontamination of different kind of surfaces. The movie will explain how to ignite the plasma solely by microwave power without any additional igniters, e.g., electric sparks. The microwave plasma torch is based on a combination of two resonators &#8212; a coaxial one which provides the ignition of the plasma and a cylindrical one which guarantees a continuous and stable operation of the plasma after ignition. The plasma can be operated in a long microwave transparent tube for volume processes or shaped by orifices for surface treatment purposes.

This movie shows how an atmospheric plasma torch can be ignited by microwaves with no additional igniters and provides a stable and continuous plasma operation suitable for plenty of applications.

This movie shows how an atmospheric pressure plasma torch can be ignited by microwave power with no additional igniters. After ignition of the plasma, a ...

How to Build a Vacuum Spring-transport Package for Spinning Rotor Gauges

The spinning rotor gauge (SRG) is a high-vacuum gauge often used as a secondary or transfer standard for vacuum pressures in the range of 1.0 x 10-4 Pa to 1.0 Pa. In this application, the SRGs are frequently transported to laboratories for calibration. Events can occur during transportation that change the rotor surface conditions, thus changing the calibration factor. To assure calibration stability, a spring-transport mechanism is often used to immobilize the rotor and keep it under vacuum during transport. It is also important to transport the spring-transport mechanism using packaging designed to minimize the risk of damage during shipping. In this manuscript, a detailed description is given on how to build a robust spring-transport mechanism and shipping container. Together these form a spring-transport package. The spring-transport package design was tested using drop-tests and the performance was found to be excellent. The present spring-transport mechanism design keeps the rotor immobilized when experiencing shocks of several hundred g (g = 9.8 m/sec2 and is the acceleration due to gravity), while the shipping container assures that the mechanism will not experience shocks greater than about 100 g during common shipping mishaps (as defined by industry standards).

Here we describe how to build a robust spring-transport mechanism for a spinning rotor gauge. This device securely immobilizes the rotor and keeps it under vacuum during transportation. We also describe packaging that minimizes the risk of damage during transport. Tests show our design works for typical shocks during transport.

The spinning rotor gauge (SRG) is a high-vacuum gauge often used as a secondary or transfer standard for vacuum pressures in the range of 1.0 x 10-4 Pa to ...

Preparation of Liquid-exfoliated Transition Metal Dichalcogenide Nanosheets with Controlled Size and Thickness: A State of the Art Protocol

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. Layered crystals of molybdenum disulphide (MoS2) and tungsten disulphide (WS2) are exfoliated in aqueous surfactant solution by sonication. This yields highly polydisperse mixtures containing nanosheets with broad size and thickness distributions. However, for most purposes, specific sizes (in terms of both lateral dimension and thickness) are required. For example, large and thin nanosheets are desired for (opto) electronic applications, while laterally small nanosheets are interesting for catalytic applications. Therefore, post-exfoliation size selection is an important step that we address here. We provide a detailed protocol on the efficient size selection in large quantities by liquid cascade centrifugation and the size and thickness quantification by statistical microscopic analysis (atomic force microscopy and transmission electron microscopy). The comparison of MoS2 and WS2 shows that both materials are size-selected in a similar way by the same procedure. Importantly, the dispersions of size-selected nanosheets show systematic changes in their optical extinction spectra with size due to edge and confinement effects. We show how these optical changes are related quantitatively to the nanosheets dimensions and describe how mean nanosheets length and layer number can be extracted reliably from the extinction spectra. The exfoliation and size selection protocol can be applied to a broad range of layered crystals as we have previously demonstrated for graphene, gallium sulphide (GaS) and black phosphorus.

A protocol for the liquid exfoliation of layered materials to nanosheets, their size selection and size measurement by microscopic and spectroscopic techniques is presented.

We summarize recent advances in the production of liquid-exfoliated transition metal dichalcogenide (TMD) nanosheets with controlled size and thickness. ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

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 ...