Zheng thanks Prof. A. Paul Alivisatos and Dr. Ulrich Dahmen for helpful
discussions during the early development of EM liquid cells. She is grateful to the support of
DOE Office of Science Early Career Research Program.

1. Microfabrication of Liquid Cells
<ol>
	<li>Prepare silicon wafers (p-doped, 100 &mu;m in thickness and 4 inches in diameter) and clean the wafers using a standard wafer bath cleaning procedure.</li>
	<li>Deposit low-stress silicon nitride thin films (20 nm in thickness) on both sides of the silicon wafers by low-pressure chemical vapor deposition (LPCVD) method. A custom developed recipe is used for the deposition, which allows the growth of silicon-rich nitride (SiNx, x&lt;4/3).</li>
	<li>Fabricate the bottom chip (2.6 &times; 2.6 mm; 3 mm in diameter) with a viewing window (1 &times; 50 &mu;m) and the top chip (2.6 &times; 2.6 mm; 3 mm in diameter) with a viewing window (1 &times; 50 &mu;m) and two reservoirs (0.6 &times; 1.2 &times; 0.1 mm) by following a sequence of standard fabrication processes, including photolithographic patterning, plasma etching of the SiNx membrane (using SF6 as the active gas), KOH wet etching of the exposed silicon wafer, etc. We use the most common photolithographic process, such as spin coating of a photoresist (positive photoresist with spin speed of 3,000 rpm for 1 min; the thickness of the photoresist is roughly 1 &mu;m), UV exposure under the Cr mask of liquid cells, lithographic patterning using developer and fixer (deionized water), etc. There are different choices of the photoresist for spin coating and the developer for patterning. And, the corresponding parameters for the processes may also vary. Since features of the pattern are relatively large (hundreds of &mu;m or larger), the process is easy to be accomplished. The KOH solution is prepared by dissolving potassium hydroxide power into deionized water with the potassium hydroxide:water weight ratio of 1:2. The KOH solution is maintained at 80 &deg;C during etching. An etching rate of 1 &mu;m per min can be achieved. SiNx membrane is an ideal protective mask for KOH etching of silicon. Since etching lines are used, individual chips are connected with thin lines of etched wafer after KOH etching. Pieces of chips can be easily separated from the wafer using sharp tweezers for subsequent processes. No dicing process is needed.</li>
	<li>Deposit indium spacer on the flat side of the bottom chip. First, do lithographic patterning of the chips by following the similar process in 1.3. To assist handling of the chips, stick individual chips (can be a piece of several chips) on a thin glass sheet using photoresist and let it air dry for 5 mins before spin coating, UV exposure, etc. Second, clean the patterned chips by O2 plasma cleaning at 50 Watts for 1 min; Third, deposit indium thin film with the thickness of 100 nm on the chip by using an evaporator; Third, lift-off process is carried out to generate the indium spacer.</li>
	<li>Bond the bottom and top chips together. We first align two silicon nitride viewing windows of the bottom and top chips under an optical microscope and apply a pressure of about 0.1 MPa by using a clamp. It requires practice in order to precisely align the windows on top of each other. Subsequently, liquids cells are baked in a vacuum oven at 120 &deg;C for 1 hr. Lastly, we collect the cells and store the as-prepared cells in a vacuum desiccator for future usage.</li>
</ol>
The whole fabrication process is shown in Figure 1. We conduct all the fabrication processes at the Nanofabrication Lab of the University of California, Berkeley.
2. Preparation of Reaction Solutions
We prepare the reaction solutions for the growth Pt3Fe nanorods as an example. Platinum (II) acetylacetonate (20 mg/ml) and Iron (II) acetylacetonate (20 mg/ml) were dissolved in a solvent mixture of pentadecane and oleylamine (7:3 vol/vol) or a mixture of pentadecane, oleylamine, and oleic acid (6:3:1 vol/vol/vol) is used for the comparison of surfactant effects.
3. Load Reaction Solutions
<ol>
	<li>About 50 nl of reaction solution is loaded into one of the reservoirs in a liquid cell by using a syringe and Teflon nanotubes (purchased from Cole-Parmer, IL). Then, the other reservoir is filled in the same manner.</li>
	<li>About 30 pl of the reaction solution is drawn into the cell by capillary force and forms a liquid layer (~100 nm) sandwiched between two silicon nitride membranes in the viewing window.</li>
	<li>The liquid cell is subsequently sealed using a thin copper cover (~50 &mu;m TEM grid with single slot 0.6 mm diameter hole, which was purchased from Tedd Pella, Inc.). Vacuum grease was applied on one-side of the cover and epoxy was used to seal the edge of the liquid cell. The total thickness of the final liquid cell is about 250-300 &mu;m.</li>
</ol>
4. Load Liquid Cells into TEM
<ol>
	<li>A JEOL 3010 TEM operated at 300 kV and a FEI monochromated F20 UT Tecnai operated at 200 kV are used for in situ imaging.</li>
	<li>The liquid cell is loaded into the microscope as a standard TEM sample for imaging.</li>
</ol>
5. Real Time TEM Imaging
<ol>
	<li>Tune the microscope to a perfect high resolution TEM imaging condition, and a beam current density of 1-8 &times; 105 A/m2 is maintained during the real-time imaging.</li>
	<li>For PtFe system, nucleation and growth of the nanoparticles can be initiated by casting the electron beam on the liquid layer.</li>
	<li>VirtualDub software combined with Gatan DigitalMicrograph software is utilized to record the nanoparticle dynamics.</li>
</ol>

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No conflicts of interest declared.

All fabrication processes have been done in the clean room, where semiconductor devices are made.
Before the deposition of indium, O2 plasma cleaning of the chips is necessary to eliminate the organic residue on the surface. Thus, a high quality indium spacer can be achieved, which can improve the bonding of top and bottom chips and the yield of leakage free liquid cells.
The silicon nitride viewing windows with ultrathin membrane of about 13 nm thick i...

The study of chemical reactions in liquids in real time and imaging biological materials in their native environment have been of significant interests across the research fields1-5. Due to the high spatial resolution of transmission electron microscopy (TEM), imaging through liquids using TEM has attracted a lot of attention4,5. However, it has been a great challenge to image liquid samples using TEM, since the conventional microscope is operated in a high vacuum environment. In addition, liquid samples have to be thin enough to allow the electron beam to go through. Williamson et al.6 reported that imaging of electrochemical deposition of Cu can be achieved with 5 nm resolution using an electrochemical liquid cell operated in a TEM. De Jonge et al.1 was able to image biological samples through serveral micrometer thick water using a scanning(S) TEM. The low contrast of the biological samples was not raised as an issue since gold nanoparticles were used as markers for imaging. The thick liquid sample was not a problem either since STEM imaging mode was used and nanometer resolution was achieved. We recently developed a self-contained liquid cell, which allows real time TEM imaging of colloidal nanoparticles in liquids with subnanometer resolution5,7. These newly developed liquid cells, which offer improved resolution and faster TEM imaging (30 frames per second that has not been achieved by high resolution STEM imaging), made it possible to study colloidal nanoparticle dynamics in liquids. The liquid cells fit in a standard TEM holder and can be operated as regular TEM samples. A small amount of liquid (about 30 picoliters) can be examined in situ under an extended chemical reaction. Various imaging and analytical (i.e., energy-dispersive X-ray spectroscopy) techniques can be applied. Since the total thickness of the viewing window (including membranes and the liquid layer) can be controlled to 100 nm or below, direct imaging of biological samples (i.e. proteins) in liquid water without gold nanoparticle markers has also been achieved 8.
In the past two decades, there have been significant achievements on the syntheses and applications of colloidal nanocrystals9-11. However, the understanding of how nanoparticles nucleate, grow and interact with each other in liquids is largely empirical and mostly based on ex situ analyses11-13. Our development of liquid cell TEM provides a unique platform to study the dynamic processes of nanoparticles in liquids in situ5,7,14,15.
We fabricate a self-contained liquid cell using ultra thin silicon wafers (100 &mu;m) by a sequential microfabrication process. It includes deposition of silicon nitride membrane, photolithographic patterning, wafer etching, spacer deposition, and cell bonding, etc. About 50 nanoliters of the reaction solution is loaded into a reservoir, which is drawn into the cell by capillary force. We fill the other reservoir with another 50 nanoliters of the liquid. Subsequently, the cell is sealed and loaded into the microscope for in situ imaging. Inside the microscope, the liquid sandwiched between two silicon nitride membranes (total about 30 picoliters) can be examined. When the electron beam passes through the thin liquid layer, dynamic processes of nanoparticles in liquids can be monitored in real time. Nucleation and growth of nanoparticles can be induced by the electron beam in some cases5,7 or reactions can be triggered by an external heating source14,16. When the electron beam damage is of a concern, low electron beam current (dose) should be used.
Since liquid cells are fabricated from silicon microfabrication processes and in large batches, variations in membrane or liquid thickness among individual liquid cells can be small6. Any researcher who has basic microfabrication training can successfully make liquid cells. The liquid handling technique and in situ TEM operation can also be mastered after practice. It is noted that besides using silicon nitride membranes as the viewing windows, other materials such as silicon dioxide, silicon or carbon (including graphene) can be used as the membrane window as well17-19. Since our liquid cells using small viewing windows, i.e., 1 x 50 &mu;m, no bulging of the membranes has been observed. And, the liquid cell is also robust to operate, i.e. below 1% of liquid cells have broken windows during the experiments. In addition, thickness of the liquid layer can also be flexibly tuned by changing the thickness of the deposited indium spacer. During sample preparation, a sealed liquid cell can maintain liquids for several days with no leakage. The small amount of liquid can be examined for several hours under the electron beam, which allows the study of an extended chemical reaction in real time.
So far, we have visualized many unique dynamic processes of nanoparticles in liquids, for example, growth and coalescence of Pt nanoparticles5,15, diffusion of nanoparticles in thin liquids20,21, growth fluctuation of Bi nanoparticles14, and growth of Pt3Fe nanorods from nanoparticle building blocks7, etc. In addition, we have also applied this method to other areas, e.g., imaging proteins in liquid water with 2.7 nm resolution8. In summary, our liquid cell TEM technique has been proven to be a very valuable development for the study of a wide range of fundamental issues in materials science, physics, chemistry and biology. We believe there is still large room for future technical advances and applications of the liquid TEM and it will certainly be a high impact on a broad spectrum of scientific research.

<table border="1">
	<tbody>
 	<tr>
 	<td></td>
 <td></td>
 <td></td>
 <td>Reagents</td>
 </tr>
 <tr>
 	<td>Platinum(II) acetylacetonate</td>
 <td>Aldrich</td>
 <td>523038</td>
 <td></td>
 </tr>
 <tr>
 	<td>Iron(II) acetylacetonate</td>
 <td>Aldrich</td>
 <td>413402</td>
 <td></td>
 </tr>
 <tr>
 	<td>pentadecane</td>
 <td>Aldrich</td>
 <td>P3406</td>
 <td></td>
 </tr>
 <tr>
 	<td>oleylamine</td>
 <td>Aldrich</td>
 <td>O7805</td>
 <td></td>
 </tr>
 <tr>
 	<td>oleic acid</td>
 <td>Sigma</td>
 <td>O4137</td>
 <td></td>
 </tr>
 <tr>
 	<td></td>
 <td></td>
 <td></td>
 <td>Equipment</td>
 </tr>
 <tr>
 	<td>TEM</td>
 <td>JEOL</td>
 <td>JEOL 3010</td>
 <td></td>
 </tr>
 <tr>
 	<td>Monochromated TEM</td>
 <td>FEI</td>
 <td>F20 UT Tecnai</td>
 <td></td>
 </tr>
 </tbody>
</table>

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.

By using liquid cell TEM method, we have visualized the solution growth of Pt3Fe nanorods from nanoparticle building blocks. Figure 2 shows sequential images depicting the growth trajectory of a Pt3Fe nanorod in different solution conditions. False coloring process using Photoshop was employed to highlight the nanoparticles.
When the solvent mixture of pentadecane and oleylamine (7:3 vol/vol) was used, three distinct stages of growth can be identified (<s...

Watch this Scientific Journal Video about Revealing Dynamic Processes of Materials in Liquids Using Liquid Cell Transmission Electron Microscopy at JoVE.com

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

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 ...

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12.6K Views.  Lawrence Berkeley National Laboratory. 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.

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

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

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

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

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

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

The optical, electrical, and structural properties of dislocations and of grain boundaries in semiconductor materials can be determined by experiments performed in a scanning electron microscope. Electron microscopy has been used to investigate cathodoluminescence, electron beam induced current, and diffraction of backscattered electrons.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications ...

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 ...

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

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

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

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

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 ...

A Method for Obtaining Serial Ultrathin Sections of Microorganisms in Transmission Electron Microscopy

Observing cells and cell components in three dimensions at high magnification in transmission electron microscopy requires preparing serial ultrathin sections of the specimen. Although preparing serial ultrathin sections is considered to be very difficult, it is rather easy if the proper method is used. In this paper, we show a step-by-step procedure for safely obtaining serial ultrathin sections of microorganisms. The key points of this method are: 1) to use the large part of the specimen and adjust the specimen surface and knife edge so that they are parallel to each other; 2) to cut serial sections in groups and avoid difficulty in separating sections using a pair of hair strands when retrieving a group of serial sections onto the slit grids; 3) to use a 'Section-holding loop' and avoid mixing up the order of the section groups; 4) to use a 'Water-surface-raising loop' and make sure the sections are positioned on the apex of the water and that they touch the grid first, in order to place them in the desired position on the grids; 5) to use the support film on an aluminum rack and make it easier to recover the sections on the grids and to avoid wrinkling of the support film; and 6) to use a staining tube and avoid accidentally breaking the support films with tweezers. This new method enables obtaining serial ultrathin sections without difficulty. The method makes it possible to analyze cell structures of microorganisms at high resolution in 3D, which cannot be achieved by using the automatic tape-collecting ultramicrotome method and serial block-face or focused ion beam scanning electron microscopy.

This study presents reliable and easy procedures for obtaining serial ultrathin sections of a microorganism without expensive equipment in transmission electron microscopy.

Observing cells and cell components in three dimensions at high magnification in transmission electron microscopy requires preparing serial ultrathin ...

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

An experimentally accessible analog method for studying molecular hydrodynamic processes in dense fluids is presented. The technique uses particle image velocimetry of vibrated, high-restitution grain piles and allows direct, macroscopic observation of dynamical processes known and predicted to exist in strongly interacting, high density gases and liquids.

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a ...

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 ...

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different materials show variability in resistive switching properties due to the intrinsic nature of the material used, leading to discrepancies in the field because of underlying operation mechanisms. This highlights a need for a reliable technique to understand mechanisms using nanostructural observations. This protocol explains a detailed process and methodology of in&#160;situ nanostructural analysis as a result of electrical biasing using transmission electron microscopy (TEM). It provides visual and reliable evidence of underlying nanostructural changes in real time memory operations. Also included is the methodology of fabrication and electrical characterizations for asymmetric crossbar structures incorporating amorphous vanadium oxide. The protocol explained here for vanadium oxide films can be easily extended to any other materials in a metal-dielectric-metal sandwiched structure. Resistive switching crossbars are predicted to serve the programmable logic and neuromorphic circuits for next-generation memory devices, given the understanding of the operation mechanisms. This protocol reveals the switching mechanism in a reliable, timely, and cost-effective way in any type of resistive switching materials, and thereby predicts the device&#39;s applicability.

In Situ Transmission Electron Microscopy with Biasing and Fabrication of Asymmetric Crossbars Based on Mixed-Phased a-VOx

Presented here is a protocol for analyzing nanostructural changes during in&#160;situ biasing with transmission electron microscopy (TEM) for a stacked metal-insulator-metal structure. It has significant applications in resistive switching crossbars for the next generation of programmable logic circuits and neuromimicking hardware, to reveal their underlying operation mechanisms and practical applicability.

Resistive switching crossbar architecture is highly desired in the field of digital memories due to low cost and high-density benefits. Different ...

Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope

Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at length scales down to the atomic level. In situ closed-cell gas reaction (CCGR) studies performed using (scanning) transmission electron microscopy (STEM) can separate and identify localized dynamic reactions, which are extremely challenging to capture using other characterization techniques. For these experiments, we used a CCGR holder that utilizes microelectromechanical systems (MEMS)-based heating microchips (hereafter referred to as &#34;E-chips&#34;). The experimental protocol described here details the method for performing in situ gas reactions in dry and wet gases in an aberration-corrected STEM. This method finds relevance in many different materials systems, such as catalysis and high-temperature oxidation of structural materials at atmospheric pressure and in the presence of various gases with or without water vapor. Here, several sample preparation methods are described for various material form factors. During the reaction, mass spectra obtained with a residual gas analyzer (RGA) system with and without water vapor further validates gas exposure conditions during reactions. Integrating an RGA with an in situ CCGR-STEM system can, therefore, provide critical insight to correlate gas composition with the dynamic surface evolution of materials during reactions. In situ/operando studies using this approach allow&#160;for detailed investigation of the fundamental reaction mechanisms and kinetics that occur at specific environmental conditions (time, temperature, gas, pressure), in real-time, and at high spatial resolution.

Performing In Situ Closed-Cell Gas Reactions in the Transmission Electron Microscope

Here, we present a protocol for performing in situ TEM closed-cell gas reaction experiments while detailing several commonly used sample preparation methods.

Gas reactions studied by in situ electron microscopy can be used to capture the real-time morphological and microchemical transformations of materials at ...