The University of Nevada, Las Vegas (UNLV) High Pressure Science and Engineering Center is supported by Department of Energy-National Nuclear Security Administration (NNSA) Cooperative Agreement DE-NA0001982. This work was performed at the High Pressure Collaborative Access Team (HPCAT) (Sector 16), and at the GeoSoilEnviroCARS (GSECARS) (Sector 13), Advanced Photon Source (APS), Argonne National Laboratory (ANL). HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974 and DOE-BES under Award No. DE-FG02-99ER45775, with partial instrumentation funding by NSF. GeoSoilEnviroCARS is supported by the National Science Foundation&#8212;Earth Sciences (EAR-0622171) and Department of Energy (DOE)&#8211;Geosciences (DE-FG02-94ER14466). APS is supported by DOE-BES, under Contract DE-AC02-06CH11357. We thank GSECARS and COMPRES for the use of the Gas Loading System.

1. Diamond Anvil Cell and Gasket Preparation
<ol>
	<li>Select a pair of diamond anvils with conical design12 and matching culet size. The conical anvil design is chosen for the wide angular x-ray windows it provides, allowing to collect relatively high resolution x-ray microdiffraction data. The culet (flat or beveled tip of a diamond anvil) is selected according to the maximum target pressure. The diameter of the flat part of the culet ranges from about 1-0.07 mm for target pressures from 10 to more than 200 GPa, respectively.</li>
	<li>Position a diamond anvil in the matching conical housing of a tungsten carbide seat and place the two in a mounting jig. Make sure that the bottom cone of the diamond anvil is firmly sitting in the tungsten carbide seat by rotating the anvil with tweezers.</li>
	<li>Apply load (few kg) on the diamond. No gap should remain between the diamond and the seat. Apply a small amount of glue around the anvil outer circumference.</li>
	<li>Cure for 1 hr at 120 &#176;C. Repeat the operation for the second diamond and seat.</li>
	<li>Insert the pair of seats with glued diamonds in the two parts of a diamond anvil cell. Bring the diamond tips (culet) in close proximity (about 30 &#181;m distance).</li>
	<li>Using a stereoscopic microscope and inspecting the anvils sideways, align the flat tips of the diamond anvils (culets) laterally using the DAC lateral set screws (Figure 1a).</li>
	<li>Gently, bring the diamond tips in contact. Use the interference fringes (Figure 1b), visible in axial stereoscopic view, to monitor the anvils relative tilt.</li>
	<li>Rock the top anvil using the DAC top screws. Fringes becoming wider and &#34;moving out of the culet&#34; (Figure 1c) indicate that the diamonds relative tilt is decreasing. In axial view, adjust the horizontal alignment (Figure 1d) using the DAC lateral set screws. Aligned diamonds show no interference fringes and overlapping edges (Figure 1e). Clean the diamonds thoroughly using acetone.</li>
	<li>Position a small metal foil, acting as gasket, between the tips of two aligned diamonds and attach the foil to the DAC body with waxy material. Suggested gasket materials include high yield strength metals such as rhenium, stainless steel or tungsten. Typical foil size is about 5 mm x 5 mm square with a thickness of 0.15-0.25 mm. The gasket should have fine texture and be free of cracks.</li>
	<li>While monitoring the total thickness of the DAC with a micrometer, turn the DAC bolts evenly and in small steps producing an indentation of a thickness that varies with the culet size in the range of about 80-20 &#181;m (Figure 2a).</li>
	<li>Drill a hole in the center of the indentation of diameter between 1/2 and 1/3 of the culet size using a laser drilling system (Figure 2b) or an EDM machine13. The gasket-hole should be centered in the indentation and be perpendicular to it.</li>
	<li>Carefully clean the gasket using a needle and ultrasonic bath for about 5 min in ethanol.</li>
	<li>Clean the diamond tips carefully using sandpaper first and then acetone dipped wipes. Reposition the gasket firmly, using waxy material, on one anvil tip.</li>
</ol>
2. Sample and Gas Loading
<ol>
	<li>The ruby fluorescence spectral shift14, 15, 16 and the gold compressibility17 are used as secondary pressure gauges. Using a fine tip tungsten needle, handpick one or two ruby spheres (~10 &#181;m in diameter) and place them on the walls of the gasket-hole, repeat the operation for a small amount of fine gold powder (Figure 2c). The pressure standards positioned on the gasket should not come in contact with the sample to avoid unwanted reactions and parasitic scattering effects. Perform all sample loading operations without the aid of bonding materials, small grains adhere weakly to the needle, the gasket or the diamond by electrostatic forces.</li>
	<li>Using an electronic balance, weigh the pure reagents, mix thoroughly appropriate proportions using a mortar.</li>
	<li>Place a small amount of the mixture between the tips of two aligned diamonds of a second DAC. Press the sample squeezing the cell by hand. The powder will be compacted in a foil about 10 &#181;m thick. Due to the small size of the sample, if the starting material is a powder mixture, as in the case of Fe4O5, it is difficult to load exact proportions, it is therefore essential that the starting powders are very fine (below 1 &#181;m) and very well mixed.</li>
	<li>Carefully, with the fine tip tungsten needle, break the foil of compacted powder into pieces. Select a flake about 40 &#181;m large. Note: The size of the loaded sample should be smaller than the size of the sample chamber at the target pressure. The sample chamber shrinks according to the assembly design and materials, and the compressibility of the materials filling the sample chamber, which is very high for the Ne and He media we use. A sample chamber starting 40 &#181;m thick and 120 &#181;m large loaded with pressurized Ne (see below) shrinks to about 15 &#181;m thickness and 70 &#181;m diameter at 20 GPa.</li>
	<li>Transfer the flake on the center of the diamond culet in the first DAC. Reassemble the two parts of the DAC (Figure 2c).</li>
	<li>Besides the absorbance of the particular laser wavelength used, the sample heating efficiency crucially depends on the sample preparation. In particular it is important to load a sample with uniform thickness that should be well insulated from diamonds and gasket. It is crucial to ensure that the sample does not adhere to the thermal conductive diamonds, which would dissipate the heat. Few grains of loose powder that almost inevitably end up around the pressed flake are usually sufficient to keep the sample lifted from the anvils. The pressure-transmitting medium will then provide a thermal insulating layer.</li>
	<li>Fill the sample chamber with a pressure-transmitting medium. Recommended media include pre-pressurized (1.7 kbar) Ne or He as these two inert media provide quasi-hydrostatic conditions to very high pressure in addition to thermal insulation. Perform the gas loading using the COMPRES/GSECARS gas loading system, described in detail elsewhere18.</li>
</ol>
3. Laser Heating and High Temperature X-ray Diffraction
Heating of a sample inside a DAC is achieved by applying infrared lasers to the sample through diamond anvils. Samples are heated to high temperatures by absorbing the laser radiation. Samples that don&#39;t absorb the 1,063 nm radiation can be mixed with absorbing and chemically inert material (example: Pt black powder) for indirect laser heating. Since diamond is a superior thermal conductor, a preferred practice is to use thermal insulation layers (example: NaCl, MgO or Al2O3) to separate the sample from the anvil surface. Absorbing and insulating materials will, however, cause additional parasitic scattering and might react with the sample.
The online laser heating systems installed in the experimental stations 16IDB of HPCAT and of 13IDD of GSECARS9, 10, 11 of the APS are designed to perform heating and x-ray diffraction on samples loaded in the DAC. Typical energies of the x-ray beam are about 30 keV and the size at the focal spot is about 5x5 &#181;m FWHM. Infrared lasers (YLF, wavelength = 1,063 nm) are used for heating samples in the DAC. A fast x-ray area detector such as MARCCD and XRD 1621 xN ESPE is utilized.
<ol>
	<li>Secure the DAC in the water cooled copper holder. Use the offline system (a remotely controlled motorized stage and a microscope) to determine the rough sample positional coordinates. The x-ray beam and the laser beams are pre-aligned to the sample position on the rotation axis of the sample stage.</li>
	<li>Mount the holder on the sample stage (Figure 3), exit and close the experimental station following the laboratory safety procedures (these are specified in the mandatory trainings required to perform experiments in the laboratory).</li>
	<li>Remotely operate the laser heating and x-ray diffraction systems from inside the experimental station, equipped with computers and monitors. Position the sample on the rotation axis of the sample stage using x-ray absorption profiles of the sample measured with an x-ray photodiode.</li>
	<li>Move the upstream and downstream laser heating optical components in the x-ray beam path.</li>
	<li>Focus the optics for clear sample viewing and adjust heating mirrors to compensate the tilting of diamond anvils.</li>
	<li>Turn on the lasers and slowly increase the laser power delivered to the sample.</li>
	<li>When the sample starts to glow (Figure 4a), collect the thermal radiation spectrum using an imaging spectrograph.</li>
	<li>Use the available software to fit the observed spectrum to the Plank radiation function assuming black body behavior to determine the sample temperature19, 20. Adjust the laser power delivered on the two sides of the sample, together or separately, to achieve the target temperature as measured on both sides of the sample.</li>
	<li>While heating the sample, collect diffraction patterns to monitor the disappearance of the starting material characteristic peaks (usually smooth Debye rings) and the appearance of the new phase peaks (usually spotty patterns). The heating time depends on the temperature and the kinetics of the particular synthesis performed. In case of the synthesis of Fe4O5 briefly described below, the synthesis is faster than this detection system (seconds).</li>
	<li>Move the sample in the plane perpendicular to the x-ray beam in steps of a few micrometers, heating the sample as uniformly as possible. Turn off the lasers and move the optical components out of the x-ray beam path.</li>
</ol>
4. X-ray Diffraction Data Collection after Synthesis
If the synthesized phase is stable after temperature quenching, diffraction data may be collected after heating. The x-ray diffraction data are collected in transmission geometry (through the anvils). Still diffraction patterns and rotation diffraction patterns (&#969;-scan) are collected. The latter are collected as single rotation images (wide scan), sets of fine step scan images (one degree or less), or large step scans images (5-10&#176;). The data collection strategy is adjusted according to the available beamtime, exposure time and detector readout speed. When using very fast detectors, fine step-scan data can be collected at each point of the 2D grid in less than an hour. This allows a complete and objective sampling of the reciprocal space across the whole sample.
<ol>
	<li>Collect a set of still diffraction images in a 2D grid distribution covering the sample area with step size similar to the x-ray beam size, about 5 &#181;m. In Figure 4b the grid of 8 x 8 = 64 images collected in a 40 &#181;m sample is shown. Typical exposure time ranges between 3-20 sec, depending on the x-ray flux and the sample scattering power.</li>
	<li>Inspect the diffraction images, select a set of locations best suited for single crystal (or multi-grain) and powder diffraction analysis. Diffraction images showing few spots are likely generated by one or few crystals that might provide good single crystal diffraction patterns. The corresponding sample locations, defined as Ay,z (with y and z being the horizontal and vertical coordinates in the plane perpendicular to the beam), are suitable for single crystal or multigrain analysis. Patterns showing smooth or, more commonly, &#34;spotty&#34; Debye rings, defined as location By,z, are suitable for powder diffraction analysis.</li>
	<li>Using the sample stage translation motors, move to the first Ay,z location. Collect a wide angle diffraction image and a set of fine step &#969;-scan diffraction images (with omega step size of 1 degree or less). Use these patterns for single-crystal or multigrain data analysis.</li>
	<li>Repeat for each selected Ay,z location.</li>
	<li>Using the sample stage translation motors, move to By,z locations. Collect wide step &#969;-scan diffraction images, i.e. 7 images with 10&#176; step size for 70&#176; total opening. Collect rotation images for powder diffraction analysis to compensate for the low grain statistics typical of LH-DAC samples.</li>
</ol>

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The authors declare no conflict of interest.

Every step of the described protocol must be performed with great care to avoid risks of experimental failure via catastrophic shatter of the anvils, gasket instability and loss of pressure, inability to achieve target temperature, sample contaminations, severe non-hydrostaticity, etc.
The greatest challenge of high P-T synthesis is the interpretation of x-ray diffraction data, a problem too extensive to be summarized here. While structural solution is inherently a non-trivial problem...

Pressure can fundamentally change the properties and bonding of matter. The Earth&#39;s topography, composition, dynamics, magnetism and even the atmosphere composition are profoundly tied to processes occurring at the interior of the planet which is under extremely high pressure and temperature. Deep Earth processes include earthquakes, volcanism, thermal and chemical convection, and differentiation. High pressure and temperature are used to synthesize super-hard materials like diamond and cubic boron nitride. High PT synthesis combined with in situ x-ray diffraction allows researchers to identify the crystal structures of the new materials or high-pressure polymorphs of extreme technological importance. The knowledge of high-pressure structures and properties allows interpretation of the structure and processes of planetary interiors, modeling of the performance of materials under extreme conditions, synthesis and design of new materials, and achievement of a broader fundamental understanding of materials&#39; behavior. The exploration of high pressure phases is technically demanding due to the twofold challenges of controllably generating extreme environmental conditions and probing small samples within bulky environmental cells.
A range of materials and techniques may be used to perform synthesis at extreme conditions2, 3. The most suitable equipment for each particular experiment depends on the material investigated, the target PT, and the probing techniques. Among high pressure devices, the LH-DAC has smallest sample size, but is however capable of reaching the highest static PT (above 5 Mbar and 6,000 K) and allows the highest resolution x-ray structural analysis. The protocol described below led to the discovery of Fe4O5 1 and is applicable to a wide range of materials and synthesis conditions. The LH-DAC is best suited for materials efficiently absorbing the laser wavelength of ~1 &#181;m available at high pressure synchrotron beamlines (e.g. 16-IDB and 13-IDD stations at the Advanced Photon Source, Argonne National Lab), for synthesis pressures up to 5 Mbar and for temperatures greater than about 1,500 K. Fairly complex structures and multiphase samples can be characterized with the x-ray microdiffraction strategies presented here. Other techniques, such as whole DAC heating4 and local resistive heating, are suitable for lower synthesis temperatures. CO2 5 laser heating, with wavelength of about 10 &#181;m, is suitable for the heating of materials transparent to the infrared YLF laser but absorbing the CO2 radiation. Other devices, such as multi-anvil, piston-cylinder and Paris-Edinburgh presses, provide larger volume samples necessary for neutron diffraction experiments, for instance.
In the LH-DAC, invented in 19676, 7, 8, high pressure is generated on a small sample placed between the tips of two opposed diamond anvils. In the laser heating systems installed at synchrotron experimental stations9, 10, 11, laser beams are delivered on a sample from both sides through the diamond anvils while a brilliant x-ray beam is focused on the heated spot. Samples absorbing the laser light are heated while x-ray diffraction is used to monitor the progress of the synthesis. The thermal radiation emitted by the laser heated sample is temperature dependent. Thermal emission spectra collected from both sides of the sample are used to calculate the sample temperature by fitting the spectra to the Plank radiation function assuming black body behavior8.
The crystal structure analysis of products of synthesis in a LH-DAC is carried out using the brilliant synchrotron x-ray beam, high precision motorized stages and the fast x-ray detectors available at dedicated synchrotron experimental stations. We collect x-ray diffraction data in a 2D grid and customize the data collection strategy according to the grain size. This approach allows to: i) map the sample composition; ii) obtain robust data analysis of a complex multiphase sample by combining single crystal, powder and multi-grain diffraction techniques.

<table border="0" cellpadding="0" cellspacing="0" width="568">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">diamond anvils</td>
			<td style="width:119px;">Almax Easylab</td>
			<td style="width:136px;">N/A</td>
			<td style="width:119px;"></td>
		</tr>
		<tr height="105">
			<td height="105" style="height:105px;width:195px;">WC seats</td>
			<td style="width:119px;">Almax Easylab</td>
			<td style="width:136px;">N/A</td>
			<td style="width:119px;">The conical housing needs to match the conical shape of the anvil bottom</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">SX-165 CCD</td>
			<td style="width:119px;">Marresearch</td>
			<td style="width:136px;"></td>
			<td style="width:119px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">XRD 1621 xN ES</td>
			<td style="width:119px;">Perkin Elmer</td>
			<td style="width:136px;"></td>
			<td style="width:119px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">W needle</td>
			<td style="width:119px;">Ted pella, Inc</td>
			<td style="width:136px;">MT26020</td>
			<td style="width:119px;"></td>
		</tr>
	</tbody>
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synthesis and microdiffraction at extreme pressures and temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

We show representative microdiffraction data obtained from the high pressure and temperature synthesis of Fe4O5 from a mixture of hematite and iron according to the reaction:
<img src="/files/ftp_upload/50613/50613eq1.jpg" alt="Equation 1" width="450px" fo:content-width="4in" />
Figure 5 illustrates powder diffraction patterns from B locations. Although they were collected a few microns apart, the patterns are remarkably differ...

Watch this Scientific Journal Video about Synthesis and Microdiffraction at Extreme Pressures and Temperatures at JoVE.com

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

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Universidad de Cartagena UDEC

Research

JoVE Journal

Engineering

11.1K Views.  University of Nevada, Las Vegas. The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

Video: Synthesis and Microdiffraction at Extreme Pressures and Temperatures

Micropunching Lithography for Generating Micro- and Submicron-patterns on Polymer Substrates

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of low weight, easy tailoring of properties and a wide spectrum of applications2,3. Due to sensitivity of conducting polymers to environmental conditions (e.g., air, oxygen, moisture, high temperature and chemical solutions), lithographic techniques present significant technical challenges when working with these materials4. For example, current photolithographic methods, such as ultra-violet (UV), are unsuitable for patterning the conducting polymers due to the involvement of wet and/or dry etching processes in these methods. In addition, current micro/nanosystems mainly have a planar form5,6. One layer of structures is built on the top surfaces of another layer of fabricated features. Multiple layers of these structures are stacked together to form numerous devices on a common substrate. The sidewall surfaces of the microstructures have not been used in constructing devices. On the other hand, sidewall patterns could be used, for example, to build 3-D circuits, modify fluidic channels and direct horizontal growth of nanowires and nanotubes.
A macropunching method has been applied in the manufacturing industry to create macropatterns in a sheet metal for over a hundred years. Motivated by this approach, we have developed a micropunching lithography method (MPL) to overcome the obstacles of patterning conducting polymers and generating sidewall patterns. Like the macropunching method, the MPL also includes two operations (Fig. 1): (i) cutting; and (ii) drawing. The "cutting" operation was applied to pattern three conducting polymers4, polypyrrole (PPy), Poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT) and polyaniline (PANI). It was also employed to create Al microstructures7. The fabricated microstructures of conducting polymers have been used as humidity8, chemical8, and glucose sensors9. Combined microstructures of Al and conducting polymers have been employed to fabricate capacitors and various heterojunctions9,10,11. The "cutting" operation was also applied to generate submicron-patterns, such as 100- and 500-nm-wide PPy lines as well as 100-nm-wide Au wires. The "drawing" operation was employed for two applications: (i) produce Au sidewall patterns on high density polyethylene (HDPE) channels which could be used for building 3D microsystems12,13,14, and (ii) fabricate polydimethylsiloxane (PDMS) micropillars on HDPE substrates to increase the contact angle of the channel15.

A micropunching lithography approach is developed to generate micro- and submicron-patterns on top, sidewall and bottom surfaces of polymer substrates. It overcomes the obstacles of patterning conducting polymers and generating sidewall patterns. This method allows rapid fabrication of multiple features and is free of aggressive chemistry.

Conducting polymers have attracted great attention since the discovery of high conductivity in doped polyacetylene in 19771. They offer the advantages of ...

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (&omega;) and momentum (k) and the probability to find them in a particular state with given &omega; and k is described by the spectral function A(k, &omega;). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He3 cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.

The overall goal of this method is to determine the low-energy electronic structure of solids at ultra-low temperatures using Angle-Resolved Photoemission Spectroscopy with synchrotron radiation.

The physical properties of a material are defined by its  electronic structure. Electrons in solids are characterized by energy (&omega;)  and momentum ...

Synthesis and Operation of Fluorescent-core Microcavities for Refractometric Sensing

This paper discusses fluorescent core microcavity-based sensors that can operate in a microfluidic analysis setup. These structures are based on the formation of a fluorescent quantum-dot (QD) coating on the channel surface of a conventional microcapillary. Silicon QDs are especially attractive for this application, owing in part to their negligible toxicity compared to the II-VI and II-VI compound QDs, which are legislatively controlled substances in many countries. While the ensemble emission spectrum is broad and featureless, an Si-QD film on the channel wall of a capillary features a set of sharp, narrow peaks in the fluorescence spectrum, corresponding to the electromagnetic resonances for light trapped within the film. The peak wavelength of these resonances is sensitive to the external medium, thus permitting the device to function as a refractometric sensor in which the QDs never come into physical contact with the analyte. The experimental methods associated with the fabrication of the fluorescent-core microcapillaries are discussed in detail, as well as the analysis methods. Finally, a comparison is made between these structures and the more widely investigated liquid-core optical ring resonators, in terms of microfluidic sensing capabilities.

Fluorescent-core microcavity sensors employ a high-index quantum-dot coating in the channel of silica microcapillaries. Changes in the refractive index of fluids pumped into the capillary channel cause shifts in the microcavity fluorescence spectrum that can be used to analyze the channel medium.

This paper discusses  fluorescent core microcavity-based sensors that can operate in a microfluidic  analysis setup. These structures are based on the ...

High-Sensitivity Nuclear Magnetic Resonance at Giga-Pascal Pressures: A New Tool for Probing Electronic and Chemical Properties of Condensed Matter under Extreme Conditions

Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their electronic properties. The application of high pressure enables one to synthesize new materials, but the response of known materials to high pressure is a very useful tool for studying their electronic structure and developing theories. For example, high-pressure synthesis might be at the origin of life; and understanding the behavior of small molecules under extreme pressure will tell us more about fundamental processes in our universe. It is no wonder that there has always been great interest in having NMR available at high pressures. Unfortunately, the desired pressures are often well into the Giga-Pascal (GPa) range and require special anvil cell devices where only very small, secluded volumes are available. This has restricted the use of NMR almost entirely in the past, and only recently, a new approach to high-sensitivity GPa NMR, which has a resonating micro-coil inside the sample chamber, was put forward. This approach enables us to achieve high sensitivity with experiments that bring the power of NMR to Giga-Pascal pressure condensed matter research. First applications, the detection of a topological electronic transition in ordinary aluminum metal and the closing of the pseudo-gap in high-temperature superconductivity, show the power of such an approach. Meanwhile, the range of achievable pressures was increased tremendously with a new generation of anvil cells (up to 10.1 GPa), that fit standard-bore NMR magnets. This approach might become a new, important tool for the investigation of many condensed matter systems, in chemistry, geochemistry, and in physics, since we can now watch structural changes with the eyes of a very versatile probe.

Nuclear magnetic resonance is one of the most important spectroscopic tools. Here, the development of a new approach under high pressure, currently up to 10.1 GPa, is presented. This opens a new window into condensed matter physics and chemistry, where high-pressure research is of great importance.

Nuclear Magnetic Resonance (NMR) is one of the most important techniques for the study of condensed matter systems, their chemical structure, and their ...

Synthesis and Characterization of High c-axis ZnO Thin Film by Plasma Enhanced Chemical Vapor Deposition System and its UV Photodetector Application

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto silicon (Si) substrates via different synthesized temperatures by using plasma enhanced chemical vapor deposition (PECVD) system. The effects of different synthesized temperatures on the crystal structure, surface morphologies and optical properties have been investigated. The X-ray diffraction (XRD) patterns indicated that the intensity of (0002) diffraction peak became stronger with increasing synthesized temperature until 400 oC. The diffraction intensity of (0002) peak gradually became weaker accompanying with appearance of (10-10) diffraction peak as the synthesized temperature up to excess of 400 oC. The RT photoluminescence (PL) spectra exhibited a strong near-band-edge (NBE) emission observed at around 375 nm and a negligible deep-level (DL) emission located at around 575 nm under high c-axis ZnO thin films. Field emission scanning electron microscopy (FE-SEM) images revealed the homogeneous surface and with small grain size distribution. The ZnO thin films have also been synthesized onto glass substrates under the same parameters for measuring the transmittance.
For the purpose of ultraviolet (UV) photodetector application, the interdigitated platinum (Pt) thin film (thickness ~100 nm) fabricated via conventional optical lithography process and radio frequency (RF) magnetron sputtering. In order to reach Ohmic contact, the device was annealed in argon circumstances at 450 oC by rapid thermal annealing (RTA) system for 10 min. After the systematic measurements, the current-voltage (I-V) curve of photo and dark current and time-dependent photocurrent response results exhibited a good responsivity and reliability, indicating that the high c-axis ZnO thin film is a suitable sensing layer for UV photodetector application.

We offered a method to directly synthesize high c-axis (0002) ZnO thin film by plasma enhanced chemical vapor deposition. The as-synthesized ZnO thin film combined with Pt interdigitated electrode was used as sensing layer for ultraviolet photodetector, showing a high performance through a combination of its good responsivity and reliability.

In this study, zinc oxide (ZnO) thin films with high c-axis (0002) preferential orientation have been successfully and effectively synthesized onto ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

Resonance Raman Spectroscopy of Extreme Nanowires and Other 1D Systems

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the presence of carbon nanotubes. These nanowires are extreme in the sense that they are the limit of miniaturization of nanowires and their behavior is not always a simple extrapolation of the behavior of larger nanowires as their diameter decreases. The paper then describes the methods required to obtain Raman spectra from extreme nanowires and the fact that due to the van Hove singularities that 1D systems exhibit in their optical density of states, that determining the correct choice of photon excitation energy is critical. It describes the techniques required to determine the photon energy dependence of the resonances observed in Raman spectroscopy of 1D systems and in particular how to obtain measurements of Raman cross-sections with better than 8% noise and measure the variation in the resonance as a function of sample temperature. The paper describes the importance of ensuring that the Raman scattering is linearly proportional to the intensity of the laser excitation intensity. It also describes how to use the polarization dependence of the Raman scattering to separate Raman scattering of the encapsulated 1D systems from those of other extraneous components in any sample.

The paper describes a method for producing extreme nanowires by melt infiltration into carbon nanotubes and how 1D systems may be characterized and investigated using Resonance Raman Spectroscopy to determine vibrational and optical excitation energies.

This paper briefly describes how nanowires with diameters corresponding to 1 to 5 atoms can be produced by melting a range of inorganic solids in the ...

Colloidal Synthesis of Nanopatch Antennas for Applications in Plasmonics and Nanophotonics

We present a method for colloidal synthesis of silver nanocubes and the use of these in combination with a smooth gold film, to fabricate plasmonic nanoscale patch antennas. This includes a detailed procedure for the fabrication of thin films with a well-controlled thickness over macroscopic areas using layer-by-layer deposition of polyelectrolyte polymers, namely poly(allylamine) hydrochloride (PAH) and polystyrene sulfonate (PSS). These polyelectrolyte spacer layers serve as a dielectric gap in between silver nanocubes and a gold film. By controlling the size of the nanocubes or the gap thickness, the plasmon resonance can be tuned from about 500 nm to 700 nm. Next, we demonstrate how to incorporate organic sulfo-cyanine5 carboxylic acid (Cy5) dye molecules into the dielectric polymer gap region of the nanopatch antennas. Finally, we show greatly enhanced fluorescence of the Cy5 dyes by spectrally matching the plasmon resonance with the excitation energy and the Cy5 absorption peak. The method presented here enables the fabrication of plasmonic nanopatch antennas with well-controlled dimensions utilizing colloidal synthesis and a layer-by-layer dip-coating process with the potential for low cost and large-scale production. These nanopatch antennas hold great promise for practical applications, for example in sensing, ultrafast optoelectronic devices and for high-efficiency photodetectors.

A protocol for the colloidal synthesis of silver nanocubes and fabrication of plasmonic nanoscale patch antennas with sub-10 nm gaps is presented.

We present a method for colloidal synthesis of silver nanocubes and the use of these in combination with a smooth gold film, to fabricate plasmonic ...

A Simple Dewar/Cryostat for Thermally Equilibrating Samples at Known Temperatures for Accurate Cryogenic Luminescence Measurements

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and a CCD spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, fast sample freezing, fast alignment of the sample, accurate and stable sample temperatures, and small size and portability of the Dewar/cryostat cryogenic unit. When coupled with the fast data acquisition rates of the CCD spectrograph, this Dewar/cryostat is capable of supporting cryogenic luminescence spectroscopic measurements on luminescent samples at a series of known, stable temperatures in the 77-300 K range. A temperature-dependent study of the oxygen quenching of luminescence in a rhodium(III) transition metal complex is presented as an example of the type of investigation possible with this Dewar/cryostat. In the context of this apparatus, a stable temperature for cryogenic spectroscopy means a luminescent sample that is thermally equilibrated with either liquid nitrogen or gaseous nitrogen at a known measureable temperature that does not vary (&#916;T &#60; 0.1 K) during the short time scale (~1-10 sec) of the spectroscopic measurement by the CCD. The Dewar/cryostat works by taking advantage of the positive thermal gradient dT/dh that develops above liquid nitrogen level in the Dewar where h is the height of the sample above the liquid nitrogen level. The slow evaporation of the liquid nitrogen results in a slow increase in h over several hours and a consequent slow increase in the sample temperature T over this time period. A quickly acquired luminescence spectrum effectively catches the sample at a constant, thermally equilibrated temperature.

A simple liquid nitrogen Dewar/cryostat apparatus comprised of a small fused silica optical Dewar, a thermocouple, and a charge-coupled device (CCD) spectrograph are described. The experiments for which this Dewar/cryostat is designed require fast sample loading, freezing, and alignment, accurate and stable sample temperatures, and small size/portability.

The design and operation of a simple liquid nitrogen Dewar/cryostat apparatus based upon a small fused silica optical Dewar, a thermocouple assembly, and ...

Synthesis of Ionic Liquid Based Electrolytes, Assembly of Li-ion Batteries, and Measurements of Performance at High Temperature

The chemical instability of the traditional electrolyte remains a safety issue in widely used energy storage devices such as Li-ion batteries. Li-ion batteries for use in devices operating at elevated temperatures require thermally stable and non-flammable electrolytes. Ionic liquids (ILs), which are non-flammable, non-volatile, thermally stable molten salts, are an ideal replacement for flammable and low boiling point organic solvent electrolytes currently used today. We herein describe the procedures to: 1) synthesize mono- and di-phosphonium ionic liquids paired with chloride or bis(trifluoromethane)sulfonimide (TFSI) anions; 2) measure the thermal properties and stability of these ionic liquids by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA); 3) measure the electrochemical properties of the ionic liquids by cyclic voltammetry (CV); 4) prepare electrolytes containing lithium bis(trifluoromethane)sulfonamide; 5) measure the conductivity of the electrolytes as a function of temperature; 6) assemble a coin cell battery with two of the electrolytes along with a Li metal anode and LiCoO2 cathode; and 7) evaluate battery performance at 100 &#176;C. We additionally describe the challenges in execution as well as the insights gained from performing these experiments.

Here, we describe protocols to prepare phosphonium-based ionic liquid and lithium bis(trifluoromethane)sulfonimide salt electrolytes, and assemble a non-flammable and high temperature functioning lithium-ion coin cell battery.

The chemical instability of the traditional electrolyte remains a safety issue in widely used energy storage devices such as Li-ion batteries. Li-ion ...