This research was supported by the National Institute of Standards and Technology. Portions of the synthesis were supported by Gordon and Betty Moore Foundation&#39;s EPiQS Initiative through Grant No. GBMF9071. Portions of the characterization were supported by the US Department of Energy (DOE) award DE-SC0019154. Identification of certain commercial products and company names is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the products or names identified are necessarily the best available for the purpose.

1. Removing uranium oxide from the uranium metal
<ol>
	<li>In a fume hood, prepare three beakers that contain 1 mL of nitric acid, 5 mL of distilled water, and 5 mL of acetone, respectively.</li>
	<li>Using a saw or cutters, cut a piece of uranium metal to the desired mass.</li>
	<li>Using tweezers, place the uranium into the beaker with nitric acid. Wait for approximately 10 s for the acid to dissolve the black oxidized surface, such that the uranium appears shiny and metallic.</li>
	<li>Take out the piece of uranium from the acid, rinse it in distilled water for 5 s, and then remove the piece of uranium.</li>
	<li>Put the uranium into the beaker containing acetone for 5 s and remove it.</li>
	<li>Determine the mass of the uranium. The uranium is ready for synthesis.</li>
</ol>
2. Chemical vapor transport
<ol>
	<li>Weigh out an appropriate amount of elemental tellurium, depending on the amount of uranium previously cleaned, following an atomic ratio of uranium to tellurium of 2:3.</li>
	<li>Weigh out an appropriate amount of iodine, determined by the desired density of 1 mg/cm3 in the volume of the quartz tube to be used during synthesis. Choose a length of the tube to span the furnace, with each end sitting in one of the temperature zones. Ensure that the diameter fits well in the furnace. 
	NOTE: Samples previously reported3 were made in a quartz tube that is 11 cm long, with a 14 mm inner diameter, so that the total mass of iodine is about 17 mg.</li>
	<li>Close one end of a fused quartz tube using a torch. A hydrogen/oxygen torch works well. Use any torch that gets hot enough to soften fused quartz. Allow the tube to cool.</li>
	<li>Put all the materials into the quartz tube. Evacuate the tube using a dry vacuum pump and seal the tube with the torch.</li>
	<li>Insert the tube into a 2-zone horizontal tube furnace. When doing this, make sure to slide all the raw materials to one side of the tube, which will be the hot side.</li>
	<li>Over 12 h, heat at constant rates the hot side to 1060 &#176;C, and the other side to 1000 &#176;C. Hold the temperatures for 1 week, and then turn off the furnace to allow it to cool slowly to room temperature.</li>
</ol>
3. Molten metal flux growth
<ol>
	<li>Weigh out uranium and tellurium according to the atomic ratio of 1:3.</li>
	<li>Put all the materials in a 2 mL alumina crucible. On top of this crucible, place another 2 mL crucible, filled with quartz wool, facing downward.</li>
	<li>Close one end of a fused quartz tube using a torch. A hydrogen/oxygen torch works well. Use any torch that gets hot enough to soften the fused quartz. Allow the tube to cool.</li>
	<li>Place the two crucibles into a quartz tube having a 14 mm inner diameter. Use a dry vacuum pump to evacuate the tube and then seal the tube with the torch.</li>
	<li>Put the quartz tube into a 50 mL alumina crucible to be used as an exterior container for stability. Place these in a box furnace.</li>
	<li>Over 12 h, heat the furnace at a constant rate to 1180 &#176;C. Hold the temperature for 5 h. Cool the furnace at constant rate to 975 &#176;C for over 100 h.</li>
	<li>Prepare a centrifuge with a swing out rotor and metal buckets. At 975 &#176;C, take out the tube using furnace tongs, carefully invert it, and then put it into the centrifuge. Spin at 2500 x g (4000 rpm for these sealed quartz tube assemblies) for 10-20 s, forcing the extra liquid tellurium to separate from the UTe2 crystals and get caught in the quartz wool.</li>
	<li>Allow the tube to cool to room temperature.</li>
</ol>
4. Opening the tubes and harvesting the crystals
<ol>
	<li>Place the quartz tube into a sealed plastic bag and place it on a hard surface, such as a laboratory benchtop or a fume hood.</li>
	<li>Using a small hammer or any other blunt object, carefully crack and break the quartz tube, preferably at the end away from the crystals.</li>
	<li>Open the plastic bag and pick out the UTe2 crystals. Perform this process within an hour or so, as UTe2 is air-sensitive and noticeably degrades over the course of several hours.</li>
	<li>Rinse the crystals with 2 mL of ethanol to remove iodine.</li>
	<li>Store the UTe2 crystals under an inert atmosphere, such as inside a nitrogen glove box.</li>
</ol>

<ol>
	<li>Sau, J. D., Tewari, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Topologically+protected+surface+majorana+arcs+and+bulk+weyl+fermions+in+ferromagnetic+superconductors.">Topologically protected surface majorana arcs and bulk weyl fermions in ferromagnetic superconductors.</a> Physical Review B. 86 (10), 104509 (2012).</li><li>Fu, L., Kane, C. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Superconducting+proximity+effect+and+majorana+fermions+at+the+surface+of+a+topological+insulator.">Superconducting proximity effect and majorana fermions at the surface of a topological insulator.</a> Physical Review Letters. 100 (9), 096407 (2008).</li><li>Ran, 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=Nearly+ferromagnetic+spin-triplet+superconductivity.">Nearly ferromagnetic spin-triplet superconductivity.</a> Science. 365 (6454), 684-687 (2019).</li><li>Hayes, I. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Weyl+Superconductivity+in+UTe2.">Weyl Superconductivity in UTe2.</a> arXiv. , (2020).</li><li>Jiao, L., 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=Chiral+superconductivity+in+heavy-fermion+metal+UTe2.">Chiral superconductivity in heavy-fermion metal UTe2.</a> Nature. 579, 523 (2020).</li><li>Ran, 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=Extreme+magnetic+field-boosted+superconductivity.">Extreme magnetic field-boosted superconductivity.</a> Nature Physics. 15, 1250-1254 (2019).</li><li>Aoki, D., 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=Unconventional+superconductivity+in+heavy+fermion+UTe2.">Unconventional superconductivity in heavy fermion UTe2.</a> Journal of the Physical Society of Japan. 88, 043702 (2019).</li><li>Cairnsm, L. P., Stevensm, C. R., O'Neill, C. D., Huxley, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Composition+dependence+of+the+superconducting+properties+of+UTe2.">Composition dependence of the superconducting properties of UTe2.</a> Journal of Physics. Condensed Matter: An Institute of Physics Journal. 32 (41), 415602 (2020).</li><li>Thomas, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evidence+for+a+pressure-induced+antiferromagnetic+quantum+critical+point+in+mixed+valence+UTe2.">Evidence for a pressure-induced antiferromagnetic quantum critical point in mixed valence UTe2.</a> Science Advances. 6 (42), (2020).</li><li>Hutanu, V., 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=Low-temperature+crystal+structure+of+the+unconventional+spin-triplet+superconductor+UTe2+from+single-crystal+neutron+diffraction.">Low-temperature crystal structure of the unconventional spin-triplet superconductor UTe2 from single-crystal neutron diffraction.</a> Acta Crystallographica Section B, Structural Science, Crystal Engineering and Materials. 76, 137-143 (2020).</li><li>Sundar, 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=Coexistence+of+ferromagnetic+fluctuations+and+superconductivity+in+the+actinide+superconductor+UTe2.">Coexistence of ferromagnetic fluctuations and superconductivity in the actinide superconductor UTe2.</a> Physical Review B. 100, 140502 (2019).</li><li>Metz, T., 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=Point-node+gap+structure+of+the+spin-triplet+superconductor+UTe2.">Point-node gap structure of the spin-triplet superconductor UTe2.</a> Physical Review B. 100, 220504 (2019).</li><li>Knebel, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Field-reentrant+superconductivity+close+to+a+metamagnetic+transition+in+the+heavy-fermion+superconductor+UTe2.">Field-reentrant superconductivity close to a metamagnetic transition in the heavy-fermion superconductor UTe2.</a> Journal of the Physical Society of Japan. 88, 063707 (2019).</li><li>Braithwaite, D., 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=Multiple+superconducting+phases+in+a+nearly+ferromagnetic+system.">Multiple superconducting phases in a nearly ferromagnetic system.</a> Communications Physics. 2, 147 (2019).</li><li>Ran, 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=Enhancement+and+reentrance+of+spin+triplet+superconductivity+in+UTe2+under+pressure.">Enhancement and reentrance of spin triplet superconductivity in UTe2 under pressure.</a> Physical Review B. 101, 140503 (2020).</li><li>Nakamine, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Superconducting+properties+of+heavy+fermion+UTe2+revealed+by+125Te-nuclear+magnetic+resonance.">Superconducting properties of heavy fermion UTe2 revealed by 125Te-nuclear magnetic resonance.</a> Journal of the Physical Society of Japan. 88, 113703 (2020).</li><li>Miao, L., 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=Low+energy+band+structure+and+symmetries+of+UTe2+from+angle+resolved+photoemission+spectroscopy.">Low energy band structure and symmetries of UTe2 from angle resolved photoemission spectroscopy.</a> Physical Review Letters. , 124 (2020).</li><li>Lin, W. -. C., 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=Tuning+magnetic+confinement+of+spin-triplet+superconductivity.">Tuning magnetic confinement of spin-triplet superconductivity.</a> npj Quantum Materials. 5, 68 (2020).</li><li>Bae, 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=Anomalous+normal+fluid+response+in+a+chiral+superconductor.">Anomalous normal fluid response in a chiral superconductor.</a> arXiv. , (2019).</li></ol>

The authors declare no competing interests.

To perform chemical vapor transport, it is simplest to utilize a two-zone horizontal furnace, which can generate a temperature gradient by setting the two zones at different temperatures. Successful use of a one-zone furnace to grow superconducting samples has not yet been demonstrated. Starting materials are sealed with a hydrogen-oxygen torch in a fused quartz tube, which must be purged of air. The purging and sealing can be accomplished by connecting the tube to a manifold attached to a dry pump and an argon gas cylinder. Once prepared, this tube is placed in the furnace such that two ends of the tube span the two temperature zones. In the case of UTe2, the end of the tube containing the starting materials is placed at the hot end. The elemental uranium and tellurium react with iodine, travel down the tube as a vapor, and eventually solidify at the cold end the quartz tube in the form of single crystals. Generally, the growth of large crystals is material-dependent and can take several weeks. For UTe2, 7 days is enough to grow crystals with mm dimensions. Following the growth, the tube is removed from the furnace and opened to harvest the crystals.
The molten metal self-flux method requires a simple resistive box furnace with one temperature zone. Uranium dissolves in molten tellurium, and the solubility of UTe2 is dependent on temperature. Starting materials, elemental uranium, and tellurium, are placed in an alumina crucible. On top of this crucible, a second crucible is placed upside down, filled with quartz wool. The two crucibles are sealed in a quartz tube, which is put in a box furnace. This time, instead of generating a fixed temperature gradient over a distance, the temperature is varied as a function of time, as the furnace is slowly cooled at a fixed rate. At the highest temperature, all the uranium will be dissolved in liquid tellurium, which has a much lower melting temperature than uranium. As the furnace cools, the solubility of UTe2 decreases and UTe2 single crystals precipitate and get larger. At a temperature that is low enough to have generated sufficiently large UTe2 single crystals, but still high enough for the tellurium to remain liquid, the quartz tube is removed from the hot furnace, placed it into a centrifuge and spun, which separates the solid UTe2 from the liquid tellurium before it freezes. After that, the tube is allowed to cool to room temperature, before it is broken to collect the crystals.
Working with depleted uranium is a heavily regulated activity that requires awareness of and compliance with applicable laws. Follow all local applicable hazardous and radioactive materials safety rules, and secure necessary permission to perform this work. These rules vary by jurisdiction and institution and cannot be addressed here. However, some general principles apply that can help with the planning of research. Researchers should be trained to work with radioactive and hazardous materials. Wear necessary personal protective equipment, including gloves. Work methodically and take care to avoid the spread of radioactive material. Discard waste in labeled and approved containers.

At temperatures typically much lower than room temperature, many materials exhibit superconductivity-the fascinating macroscopic quantum state in which the electrical resistance becomes absolutely zero and electrical current can flow without dissipation. In the typical superconducting phase, instead of acting as separate entities, the constituent electrons form Cooper pairs, which are commonly made up of two electrons with opposite spins, in a spin singlet configuration. However, in very rare cases, the Cooper pairs can instead be made up of two electrons with parallel spins, in a spin triplet configuration. Among the few thousand superconductors discovered so far, there are only a few superconductors that have been identified as spin triplet candidates. This rare quantum phenomenon has attracted a lot of research interest because spin triplet superconductors are proposed to be one potential building block for quantum computers1,2, the next generation of computation technology.
Recently, Ran and coworkers reported that UTe2 is a candidate spin triplet superconductor3. This superconductor has many exotic properties indicative of a spin triplet configuration: an extreme, disproportionately large, critical magnetic field required to suppress the superconductivity, a temperature-independent NMR Knight shift3, a spontaneous magnetic moment indicated by the optical Kerr effect4, and a chiral electronic surface state indicated by scanning tunneling spectroscopy5. Moreover, additional superconducting phases are actually induced in high magnetic field6, an example of the unusual phenomenon of reentrant superconductivity.
Although these new results are robust, the superconducting properties of UTe2 depend on the synthesis process used by different groups7,8,9. Crystals of UTe2 synthesized using the chemical vapor transport method superconduct below a critical temperature of 1.6 K. In contrast, those grown using the molten flux method have a greatly suppressed superconducting critical temperature or do not superconduct at all. In anticipation of applications such as quantum computing, reliably obtaining crystals that superconduct is highly desirable. Moreover, investigating why nominally similar crystals do not superconduct is also very helpful for understanding the fundamental superconducting pairing mechanism in UTe2, which, while novel and a topic of intense research, must differ significantly from that of conventional superconductors. For these reasons, the two different synthesis methods are complementary and useful to compare. In this paper, two different methods for synthesis of UTe2 are demonstrated and properties of the single crystals from the two methods are compared.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-zone tube furnace</td>
			<td>MTI Corporation</td>
			<td>OTF-1200X-S-II-25-110</td>
			<td></td>
		</tr>
		<tr>
			<td>Alumina crucible</td>
			<td>Coorstek Inc.</td>
			<td>65530-CN-2-AD-998</td>
			<td>Size = 2 mL</td>
		</tr>
		<tr>
			<td>Box furnace</td>
			<td>MTI Corporation</td>
			<td>KSL-1500X</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Thermo Scientific</td>
			<td>Mo/No: CL2, S/N:42618752</td>
			<td></td>
		</tr>
		<tr>
			<td>Fused quartz tube</td>
			<td>Quartz Scientific</td>
			<td>100014B</td>
			<td>14 mm ID, 16 mm OD, 48&#34; length</td>
		</tr>
		<tr>
			<td>Iodine</td>
			<td>J. T. Baker Inc.</td>
			<td>2208-04</td>
			<td>Sublimed, 99.997% pure,&#160; typically approximately 14 mg</td>
		</tr>
		<tr>
			<td>Tellurium</td>
			<td>Alfa Aesar</td>
			<td>42213</td>
			<td>99.9999% pure,&#160; Typically approximately 0.5 g</td>
		</tr>
		<tr>
			<td>Uranium</td>
			<td>Dept. of Energy (NBL)</td>
			<td>CRM115</td>
			<td>Uranium (Depleted U238) Metal (0.99977 g U/g).&#160; Typically approximately 0.5 g 235U/238U = 0 +- 3.6x10-9</td>
		</tr>
	</tbody>
</table>

comparison of two different synthesis methods of single crystals of superconducting uranium ditelluride

Single crystal specimens of the actinide compound uranium ditelluride, UTe2, are of great importance to the study and characterization of its dramatic unconventional superconductivity, believed to entail spin-triplet electron pairing. A variety in the superconducting properties of UTe2 reported in the literature indicates that discrepancies between synthesis methods yield crystals with different superconducting properties, including the absence of superconductivity entirely. This protocol describes a process to synthesize crystals that exhibit superconductivity via chemical vapor transport, which has consistently exhibited a superconducting critical temperature of 1.6 K and a double transition indicative of a multi-component order parameter. This is compared to a second protocol that is used to synthesize crystals via the molten metal flux growth technique, which produces samples that are not bulk superconductors. Differences in the crystal properties are revealed through a comparison of structural, chemical, and electronic property measurements, showing that the most dramatic disparity occurs in the low-temperature electrical resistance of the samples.

Both growth techniques yield crystals of UTe2 having dimensions on the millimeter length scale. Crystals are shiny, with a metallic luster. The crystal morphology is variable, and intergrowths can occur. Generally, chemical vapor transport and flux grown crystals look similar and are not easily distinguishable by visual inspection, as is evident in Figure 1.
To confirm the crystal structure, powder x-ray diffraction measurements are typically performed on crushed single crystals of both CVT grown and flux grown UTe2 single crystals at room temperature. Single crystals from both growth techniques have the same crystal structure and are single phase, with no sign of impurity phases. Figure 2 shows the collected x-ray diffraction data and a refinement to a body-centered orthorhombic crystal structure with the space group Immm10.
The temperature dependence of the electrical resistance is a typical way to characterize metallic materials. Figure 3 compares the temperature dependence of the electric resistance, normalized to the room temperature value, for samples of UTe2 synthesized using chemical vapor transport and flux methods. These data were collected in a commercial refrigerator system using a standard 4-lead configuration. Above 50 K, both samples show a slight increase of the electrical resistance upon cooling, which is atypical of metals. This behavior is consistent with that caused by scattering of conduction electrons off the uranium atomic magnetic moments, known as the single ion Kondo effect. A broad maximum is also seen in both samples, followed by a drop in resistance due to the onset of Kondo coherence.
A distinct difference between the samples is that the value of the residual resistance, or value of the resistance in the zero-temperature limit, is dramatically larger in the sample synthesized by the flux method. The residual resistance ratio RRR, or the ratio between the resistance value at room temperature and the residual resistance, is approximately 2 for the flux grown sample, which is about 15 times smaller than the RRR value of the chemical vapor transport sample. The greatly reduced RRR of the flux grown sample indicates that there are more crystallographic impurities or defects in the flux grown sample, which are responsible for stronger scattering of the conduction electrons, and hence the higher residual resistance. These values are consistent with previous reports7.
A more dramatic difference is that the flux grown samples do not superconduct. In general, the presence of impurities and defects is detrimental to superconductivity because increased scattering weakens the electron pairing interaction that underlies superconductivity. The effects of disorder may be even more pronounced in UTe2, in which superconductivity is believed to be of the unusual spin triplet variety that is generally more sensitive to pair breaking11,12,13,14,15,16,17,18,19. The effects of disorder and chemistry on superconductivity in UTe2 are still in the early days and are currently an active field of study.
The DC magnetic susceptibility, or magnetization normalized to the applied field, of both flux grown and CVT grown UTe2 look very similar. As shown in Figure 4, in which the data were collected at 1000 Oe in a commercial SQUID magnetometer, the high-temperature magnetic susceptibility shows a paramagnetic response when the magnetic field is applied along the crystallographic a-axis of the samples. At low temperatures, the magnetic susceptibility increases sharply and then shows a slight slope change at ~10 K, likely due to the Kondo coherence. The difference between the magnetic susceptibility curves of the two samples is small and attributable to slight sample misalignment, rendering the two samples indistinguishable to this measurement.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62563/62563fig01.jpg" /> 
Figure 1: Photographs of single crystals of UTe2. (A) flux grown and (B-C) CVT grown. The grids are 1 mm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62563/62563fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62563/62563fig02.jpg" /> 
Figure 2: Powder Xray diffraction data of CVT grown UTe2. The data shows the good quality of the sample with no visible peaks from impurities. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62563/62563fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62563/62563fig3v2.jpg" /> 
Figure 3: Normalized electrical resistance data as a function of temperature for both CVT grown and flux grown UTe2. The flux grown sample has a substantially larger residual resistance, which is a signature of increased crystallographic disorder. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62563/62563fig3v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62563/62563fig4v2.jpg" /> 
Figure 4: Magnetic susceptibility, or magnetization normalized to applied magnetic field, as a function of temperature for both CVT grown and flux grown UTe2.&#160;The samples show similar behavior, including a characteristic kink at approximately 10 K. A magnetic field H = 1000 Oe is applied parallel to the crystallographic a-axis. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/62563/62563fig4v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride at JoVE.com

Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

Here, we present a protocol to synthesize two types of UTe2 crystals: those exhibiting robust superconductivity, via chemical vapor transport synthesis, and those lacking superconductivity, via molten metal flux synthesis.

Single crystal specimens of the actinide compound uranium ditelluride, UTe2, are of great importance to the study and characterization of its dramatic ...

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2.7K Views.  University of Maryland. Here, we present a protocol to synthesize two types of UTe2 crystals: those exhibiting robust superconductivity, via chemical vapor transport synthesis, and those lacking superconductivity, via molten metal flux synthesis.

Video: Comparison of Two Different Synthesis Methods of Single Crystals of Superconducting Uranium Ditelluride

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Current methods in DNA nano-architecture have successfully engineered a variety of 2D and 3D structures using principles of self-assembly. In this ...

From Constructs to Crystals &#8211; Towards Structure Determination of &#946;-barrel Outer Membrane Proteins

Membrane proteins serve important functions in cells such as nutrient transport, motility, signaling, survival and virulence, yet constitute only ~1% percent of known structures. There are two types of membrane proteins, &#945;-helical and &#946;-barrel. While &#945;-helical membrane proteins can be found in nearly all cellular membranes, &#946;-barrel membrane proteins can only be found in the outer membranes of mitochondria, chloroplasts, and Gram-negative bacteria. One common bottleneck in structural studies of membrane proteins in general is getting enough pure sample for analysis. In hopes of assisting those interested in solving the structure of their favorite &#946;-barrel outer membrane protein (OMP), general protocols are presented for the production of target &#946;-barrel OMPs at levels useful for structure determination by either X-ray crystallography and/or NMR spectroscopy. Here, we outline construct design for both native expression and for expression into inclusion bodies, purification using an affinity tag, and crystallization using detergent screening, bicelle, and lipidic cubic phase techniques. These protocols have been tested and found to work for most OMPs from Gram-negative bacteria; however, there are some targets, particularly for mitochondria and chloroplasts that may require other methods for expression and purification. As such, the methods here should be applicable for most projects that involve OMPs from Gram-negative bacteria, yet the expression levels and amount of purified sample will vary depending on the target OMP.

&#946;-barrel outer membrane proteins (OMPs) serve many functions within the outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts. Here, we hope to alleviate a known bottleneck in structural studies by presenting protocols for the production of &#946;-barrel OMPs in sufficient quantities for structure determination by X-ray crystallography or NMR spectroscopy.

Membrane proteins serve important functions in cells such as nutrient transport, motility, signaling, survival and virulence, yet constitute only ~1% ...

Synthesis and Exfoliation of Discotic Zirconium Phosphates to Obtain Colloidal Liquid Crystals

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and engineers. Growth of such anisotropic nanocrystals through a simple chemical method is a challenging task. In this study, we fabricate discotic nanodisks of zirconium phosphate [Zr(HPO4)2&#183;H2O] as a model material using hydrothermal, reflux and microwave-assisted methods. Growth of crystals is controlled by duration time, temperature, and concentration of reacting species. The novelty of the adopted methods is that discotic crystals of size ranging from hundred nanometers to few micrometers can be obtained while keeping the polydispersity well within control. The layered discotic crystals are converted to monolayers by exfoliation with tetra-(n)-butyl ammonium hydroxide [(C4H9)4NOH, TBAOH]. Exfoliated disks show isotropic and nematic liquid crystal phases. Size and polydispersity of disk suspensions is highly important in deciding their phase behavior.

A two dimensional model material of discotic zirconium phosphate was developed. The inorganic crystal with lamellar structure was synthesized by hydrothermal, reflux, and microwave-assisted methods. On exfoliation with organic molecules, layered crystals can be converted to monolayers, and nematic liquid crystal phase was formed at sufficient concentration of monolayers.

Due to their abundance in natural clay and potential applications in advanced materials, discotic nanoparticles are of interest to scientists and ...

Synthesis of Programmable Main-chain Liquid-crystalline Elastomers Using a Two-stage Thiol-acrylate Reaction

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline elastomers (LCEs) with facile control over network structure and programming of an aligned monodomain. Tailored LCE networks were synthesized using routine mixing of commercially available starting materials and pouring monomer solutions into molds to cure. An initial polydomain LCE network is formed via a self-limiting thiol-acrylate Michael-addition reaction. Strain-to-failure and glass transition behavior were investigated as a function of crosslinking monomer, pentaerythritol tetrakis(3-mercaptopropionate) (PETMP). An example non-stoichiometric system of 15 mol% PETMP thiol groups and an excess of 15 mol% acrylate groups was used to demonstrate the robust nature of the material. The LCE formed an aligned and transparent monodomain when stretched, with a maximum failure strain over 600%. Stretched LCE samples were able to demonstrate both stress-driven thermal actuation when held under a constant bias stress or the shape-memory effect when stretched and unloaded. A permanently programmed monodomain was achieved via a second-stage photopolymerization reaction of the excess acrylate groups when the sample was in the stretched state. LCE samples were photo-cured and programmed at 100%, 200%, 300%, and 400% strain, with all samples demonstrating over 90% shape fixity when unloaded. The magnitude of total stress-free actuation increased from 35% to 115% with increased programming strain. Overall, the two-stage TAMAP methodology is presented as a powerful tool to prepare main-chain LCE systems and explore structure-property-performance relationships in these fascinating stimuli-sensitive materials.

A novel methodology is presented to synthesize and program main-chain liquid-crystalline elastomers using commercially available starting monomers. A wide range of thermomechanical properties was tailored by adjusting the amount of crosslinker, while the actuation performance was dependent on the amount of applied strain during programming.

This study presents a novel two-stage thiol-acrylate Michael addition-photopolymerization (TAMAP) reaction to prepare main-chain liquid-crystalline ...

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A protocol for the synthesis and characterization of diffusive motion of cyclic polymers at the single molecule level is presented.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single ...

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity in aqueous CO2 reduction. Different from traditional metal nanocrystals, the synthesis of metal single atoms involves a matrix material that can confine those single atoms and prevent them from aggregation. We report an electrospinning and thermal annealing method to prepare Ni single atoms dispersed and coordinated in a graphene shell, as active centers for CO2 reduction to CO. During the synthesis, N dopants play a critical role in generating graphene vacancies to trap Ni atoms. Aberration-corrected scanning transmission electron microscopy and three-dimensional atom probe tomography were employed to identify the single Ni atomic sites in graphene vacancies. Detailed setup of electrochemical CO2 reduction apparatus coupled with an on-line gas chromatography is also demonstrated. Compared to metallic Ni, Ni single atom catalyst exhibit dramatically improved CO2 reduction and suppressed H2 evolution side reaction.

Synthesis and Performance Characterizations of Transition Metal Single Atom Catalyst for Electrochemical CO2 Reduction

Here, we present a protocol for the synthesis and electrochemical testing of transition metal single atoms coordinated in graphene vacancies as active centers for selective carbon dioxide reduction to carbon monoxide in aqueous solutions.

This protocol presents both the synthesis method of the Ni single atom catalyst, and the electrochemical testing of its catalytic activity and selectivity ...

Novel Techniques for Observing Structural Dynamics of Photoresponsive Liquid Crystals

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational spectroscopy and time-resolved electron diffraction. Liquid crystal phase is an important state of matter that exists between the solid and liquid phases and it is common in natural systems as well as in organic electronics. Liquid crystals are orientationally ordered but loosely packed, and therefore, the internal conformations and alignments of the molecular components of LCs can be modified by external stimuli. Although advanced time-resolved diffraction techniques have revealed picosecond-scale molecular dynamics of single crystals and polycrystals, direct observations of packing structures and ultrafast dynamics of soft materials have been hampered by blurry diffraction patterns. Here, we report time-resolved IR vibrational spectroscopy and electron diffractometry to acquire ultrafast snapshots of a columnar LC material bearing a photoactive core moiety. Differential-detection analyses of the combination of time-resolved IR vibrational spectroscopy and electron diffraction are powerful tools for characterizing structures and photoinduced dynamics of soft materials.

Here, we present the protocols of differential-detection analyses of time-resolved infrared vibrational spectroscopy and electron diffraction which enable observations of the deformations of local structures around photoexcited molecules in a columnar liquid crystal, giving an atomic perspective on the relationship between the structure and the dynamics of this photoactive material.

We discuss in this article the experimental measurements of the molecules in liquid crystal (LC) phase using the time-resolved infrared (IR) vibrational ...

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

Synthesis and Structure Determination of &#181;-Conotoxin PIIIA Isomers with Different Disulfide Connectivities

Peptides with a high number of cysteines are usually influenced regarding the three-dimensional structure by their disulfide connectivity. It is thus highly important to avoid undesired disulfide bond formation during peptide synthesis, because it may result in a completely different peptide structure, and consequently altered bioactivity. However, the correct formation of multiple disulfide bonds in a peptide is difficult to obtain by using standard self-folding methods such as conventional buffer oxidation protocols, because several disulfide connectivities can be formed. This protocol represents an advanced strategy required for the targeted synthesis of multiple disulfide-bridged peptides which cannot be synthesized via buffer oxidation in high quality and quantity. The study demonstrates the application of a distinct protecting group strategy for the synthesis of all possible 3-disulfide-bonded peptide isomers of &#181;-conotoxin PIIIA in a targeted way. The peptides are prepared by Fmoc-based solid phase peptide synthesis using a protecting group strategy for defined disulfide bond formation. The respective pairs of cysteines are protected with trityl (Trt), acetamidomethyl (Acm), and tert-butyl (tBu) protecting groups to make sure that during every oxidation step only the required cysteines are deprotected and linked. In addition to the targeted synthesis, a combination of several analytical methods is used to clarify the correct folding and generation of the desired peptide structures. The comparison of the different 3-disulfide-bonded isomers indicates the importance of accurate determination and knowledge of the disulfide connectivity for the calculation of the three-dimensional structure and for interpretation of the biological activity of the peptide isomers. The analytical characterization includes the exact disulfide bond elucidation via tandem mass spectrometry (MS/MS) analysis which is performed with partially reduced and alkylated derivatives of the intact peptide isomer produced by an adapted protocol. Furthermore, the peptide structures are determined using 2D nuclear magnetic resonance (NMR) experiments and the knowledge obtained from MS/MS analysis.

Cysteine-rich peptides fold into distinct three-dimensional structures depending on their disulfide connectivity. Targeted synthesis of individual disulfide isomers is required when buffer oxidation does not lead to the desired disulfide connectivity. The protocol deals with the selective synthesis of 3-disulfide-bonded peptides and their structural analysis using NMR and MS/MS studies.

Peptides with a high number of cysteines are usually influenced regarding the three-dimensional structure by their disulfide connectivity. It is thus ...