This work was supported by NSF Grant No. DMR-1207243, the NSF MRSEC program (DMR-0820414), DOE Grant No. DE-FG02-03ER46054, and the OSU-Institute for Materials Research. The authors acknowledge the NanoSystems Laboratory at Ohio State University, and technical assistance from C. Y. Kao and C.Y. Chen.

1. Synthesis and Preparation of Precursors
<ol>
	<li>Preparation of [Et4N][V(CO)6]23
	<ol>
		<li>In a nitrogen glovebox, cut 1.88 g of sodium metal into ~40 pieces and mix with 14.84 g of anthracene in 320 ml of anhydrous tetrahydrofuran (THF) in a 1 L three-neck round bottom flask. 
		CAUTION: Both sodium metal and tetrahydrofuran are highly flammable.</li>
		<li>Stir the solution for 4.5 hr at RT under a nitrogen atmosphere until a deep blue solution of NaC14H10 is formed.</li>
		<li>Cool the solution to 0 &#176;C.</li>
		<li>In a nitrogen glovebox, prepare a pink-red solution of VCL3(THF)3 by adding 400 ml of anhydrous THF into 7.48 g of VCl3(THF)3 in a 500 ml round bottom flask and stir at RT for 1 hr.</li>
		<li>Remove the pink-red solution VCl3(THF)3 from the glovebox and cool to 0 &#176;C for 20 min. Transfer to the previous solution of NaC14H10 via cannula under nitrogen atmosphere. A homogeneous deep purple solution is formed immediately after the addition is completed.</li>
		<li>Remove from the nitrogen and stir for 15 hr. Slowly warm to RT by placing flask in ice bucket allowing the ice to melt O/N.</li>
		<li>Cool the solution again to 0 &#176;C and fill the reaction flask with carbon monoxide. The solution will change from deep purple to yellow-brown in a matter of minutes. 
		CAUTION: Carbon monoxide is highly toxic. This step should not be performed alone and a carbon monoxide alarm should be installed in the lab.</li>
		<li>Stir the solution under a carbon monoxide atmosphere at 0 &#176;C for 15 hr and then slowly warm to RT.</li>
		<li>Remove all but 200 ml of THF under vacuum. Add 500 ml of O2 free water while stirring the solution. V(CO)6 is easily oxidized and the presence of O2 will result in a low yield.</li>
		<li>Filter the resulting yellow slurry into a solution composed of 20.8 g of tetraethylammonium bromide (Et4NBr) in 200 ml of H2O.</li>
		<li>Wash the filter cake with O2 free water until it is colorless.</li>
		<li>Filter the resulting slurry of [Et4N][V(CO)6] by vacuum filtration and dry under vacuum.</li>
		<li>Store [Et4N][V(CO)6] in a glovebox freezer for future use.</li>
	</ol>
	</li>
	<li>Preparation of V(CO)623
	<ol>
		<li>Grease the connection points for a vacuum adaptor with stopcock, glass two-way connecting tube, and cold-finger. Place a cold finger in the center neck and a vacuum adaptor with stopcock in the third opening.</li>
		<li>In an argon glovebox, mix 100 mg of [Et4N][V(CO)6] with 1 g of phosphoric acid in a round bottom flask containing a magnetic stirring bar.</li>
		<li>Connect the round bottom flask to a three-neck round bottom flask via glass two-way connecting tube in the argon glovebox.</li>
		<li>Remove the sealed flask system from the glovebox and set up in chemical hood.</li>
		<li>Add methanol to the cold finger and stir with a spatula-while adding liquid nitrogen until methanol is frozen. Pump down the system by opening the stopcock to a vacuum line until the pressure reaches 5 x 10-2 Torr.</li>
		<li>Submerge the round bottom flask in an oil bath set to 45 &#176;C and turn on the magnetic stirring. Once the reaction starts, the phosphoric acid will melt and a black-blue powder condenses on the cold finger.</li>
		<li>Open the vacuum line when a black powder condenses on the round bottom flask instead of the cold finger because the pressure is too high. Pump the system back to 5 x 10-2 Torr before closing again.</li>
		<li>Rotate the reaction flask as necessary to mix all of the reactants.</li>
		<li>Allow the reaction to continue until the remaining residue in round bottom flask is white-grey and no longer bubbling.</li>
		<li>Pour copper pellets into a cold safe container and cool with liquid nitrogen.</li>
		<li>Remove the methanol from the cold finger with a micropipette. Pour chilled copper pellets into the cold finger to keep it cold during transfer to glovebox.</li>
		<li>Wipe oil and condensed water off the flask system before transferring into an argon glovebox.</li>
		<li>Inside the glovebox, remove the cold finger from the flask system and use a spatula to scrape the black V(CO)6 powder onto a piece of weighing paper.</li>
		<li>Store V(CO)6 in a bottle under an argon atmosphere and keep below RT.</li>
	</ol>
	</li>
	<li>Purification of TCNE by sublimation
	<ol>
		<li>Purchase commercially available tetracyanoethylene (TCNE) and store in a chemical refrigerator.</li>
		<li>Mix ~5 g of TCNE with ~0.5 g of activated carbon and grind with a mortar and pestle.</li>
		<li>Place TCNE/carbon mixture into a glass boat or wrap in delicate task wipes and put in the bottom of a flask with a vacuum line.</li>
		<li>Place a cold finger into the top of the flask and seal the two parts together with a clamp.</li>
		<li>Add methanol to the cold finger and stir with a spatula-while adding liquid nitrogen until methanol is frozen. Place the bottom of the flask containing the TCNE in an oil bath heated to 70 &#176;C.</li>
		<li>Open the vacuum line to reach a pressure of 10-4 Torr and then close the vacuum line.</li>
		<li>Occasionally open the vacuum line to maintain the pressure. TCNE condenses on the cold finger as sublimation begins. Once no more TCNE accumulates on the cold finger the sublimation is finished.</li>
		<li>Remove the methanol from the cold finger with a micropipette.</li>
		<li>Wipe oil and condensed water off the flask system before transferring into an argon glovebox.</li>
		<li>Inside the glovebox, remove the cold finger from the flask system and use a spatula to scrape the TCNE powder onto a piece of weighing paper.</li>
		<li>Store purified TCNE in a refrigerator below RT under inert atmosphere.</li>
	</ol>
	</li>
</ol>
2. Set up Deposition System inside an Argon Glovebox
<ol>
	<li>Assemble the reactor inside an argon glovebox as shown in Figure 1A.
	<ol>
		<li>Set up a connection to a vacuum pump.</li>
		<li>Set up the gas flow connections by connecting a 3-way stopcock between a flow meter and two lines connected to micrometer valves.</li>
		<li>Slide the glass heater coil around the reactor (part A, Figure 1B).</li>
		<li>Wrap a glass slide with polytetrafluoroethylene (PTFE) thread seal tape.</li>
		<li>Push the glass slide approximately 10 cm from the right side of the reactor, part A.</li>
		<li>Place an O-ring on Part B and slide into the right side of the reactor. Join the two pieces together with a clamp.</li>
		<li>Attach a vacuum line to the bottom connection on part A and attach the gauge to the top connection.</li>
		<li>Place a boat filled with purified TCNE into part C near end so that the TCNE will sit in the hottest part of the reactor.</li>
		<li>Grease the connection of part C and slide it into the left side of the reactor.</li>
		<li>Grease both sides of the T-boat filled with V(CO)6 and slide into the right end of part B.</li>
		<li>Connect each micrometer valve. One should be connected to the right side of the T-boat and the other to the left side of part C and clamp both in place.</li>
		<li>Run a test deposition to determine where the reaction zone is located.</li>
	</ol>
	</li>
	<li>Deposit V[TCNE]x~2 onto substrates
	<ol>
		<li>Set the temperature of the reaction heating coil so that the reaction zone is set to a value near 46 &#176;C when measured on the bottom of the reactor and the area of the TCNE boat is near 75 &#176;C. Set the temperature of a silicone oil bath to 10 &#176;C. Allow the temperatures to stabilize for at least 30 min.</li>
		<li>Slide the glass heater coil around the reactor (part A, Figure 1A).</li>
		<li>Wrap a glass slide with polytetrafluoroethylene (PTFE) thread seal tape. Arrange samples on top of covered slide within a two-inch space.</li>
		<li>Push the glass slide into the reactor so the samples are located in the reaction zone. Alternately samples can be placed directly on the bottom of the reactor, although the reaction zone may be shifted without a glass slide.</li>
		<li>Place an O-ring on Part B and slide into the right side of the reactor. Join the two pieces together with a clamp.</li>
		<li>Attach a vacuum line to the bottom connection on part A and attach the gauge to the top connection.</li>
		<li>Put 50 mg of TCNE into the TCNE boat and 5 mg of V(CO)6 into the T-boat (these quantities are appropriate for an 75-90 min deposition).</li>
		<li>Slide the TCNE boat into part C near the end so that the TCNE will sit in the hottest part of the reactor which should be about 75 &#176;C.</li>
		<li>Grease the connection of part C and slide it into the left side of the reactor.</li>
		<li>Grease both sides of the T-boat and slide into the right end of part B.</li>
		<li>Slide the flow line onto the right side of the T-boat and left sides of part C and clamp in place. The assembled set-up should resemble Figure 1A.</li>
		<li>Raise the oil bath to cover the entire bottom of the T-boat.</li>
		<li>Open the vacuum line to reach a pressure of 30-35 mmHg.</li>
		<li>Set the flow rate to 56 sccm for the V(CO)6 and to 84 sccm for the TCNE. The reaction should begin immediately with a greenish material condensing on the wall of reaction zone.</li>
		<li>Allow reaction to proceed for the desired length of time. The thickness of the thin film is based on reaction time and location inside the reactor, as shown in Figure 2.</li>
		<li>To stop the reaction, close vacuum line and turn off the heater and oil bath.</li>
	</ol>
	</li>
</ol>
3. Clean up
<ol>
	<li>Take apart the system in any order.</li>
	<li>Soak all the glassware except the heater coil in a base bath solution for at least 1-2 hr.</li>
	<li>Rinse glassware with water and dry in an oven.</li>
</ol>
<img alt="Figure 1" src="/files/ftp_upload/52891/52891fig1.jpg" /> 
Figure 1. (A) Fully assembled custom chemical vapor deposition (CVD) system. (B) Expanded view of the components for the CVD system. <a href="https://www.jove.com/files/ftp_upload/52891/52891fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/52891/52891fig2.jpg" /> 
Figure 2. (A) A top view of the substrates in the reactor showing their location. (B) Approximate film thickness as function of position inside the reactor tube, Part A from Figure 1B for a deposition of 75 min. <a href="https://www.jove.com/files/ftp_upload/52891/52891fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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The authors have nothing to disclose.

The key parameters for V[TCNE]x~2 deposition include temperature, carrier gas flow, pressure, and ratio of precursors. Because the chemical vapor deposition set-up is not commercially available these parameters will need to be optimized for each system. A previous study by Shima et al. revealed that the temperature has the largest impact on the sublimation rate of the TCNE precursor26. The temperature can be modified both by the value set on the temperature controller and also by m...

The organic-based ferrimagnetic semiconductor vanadium tetracyanoethylene (V[TCNE]x, x~2) exhibits room temperature magnetic ordering and promises the advantages of organic materials for magnetoelectronic applications, such as flexibility, low cost production, and chemical tunability. Previous studies have demonstrated functionality in spintronic devices, including hybrid organic/inorganic1,2 and all-organic spin valves3, and as a spin polarizer in an active organic/inorganic semiconductor heterostructure4. In addition, V[TCNE]x~2 has demonstrated promise for inclusion in high frequency electronics due to its extremely narrow ferromagnetic resonance linewidth5.
There are four different methods which have been established for synthesizing V[TCNE]x~26-9. V[TCNE]x~2 was first synthesized as powder in dichloromethane via reaction of TCNE and V(C6H6)6. These powders exhibited the first room temperature magnetic ordering observed in an organic-based material. However, the powder form of this material is extremely air sensitive, limiting its application in thin film devices. In 2000, a chemical vapor deposition (CVD) method was established for creating V[TCNE]x~2 thin films7. More recently physical vapor deposition (PVD)8 and molecular layer deposition (MLD)9 have also been used to fabricate thin films. The PVD method requires an ultra-high vacuum (UHV) system and both PVD and mLD methods require extremely long times to grow films thicker than 100 nm, whereas the CVD films can easily be deposited in thicknesses ranging from 30 nm to several microns. In addition to the variety of thicknesses available with the CVD method, extensive studies have yielded optimized films that consistently show high quality magnetic properties including: narrow ferromagnetic resonance (FMR) linewidth (1.5 G), high Curie temperature (600 K), and sharp magnetic switching5.
Magnetic ordering in V[TCNE]x~2 thin films proceeds via an unconventional route. SQUID magnetometry measurements show strong local magnetic ordering, but the absence of X-ray diffraction peaks and featureless transmission electron microscopy (TEM)10 morphology reveal a lack of long-range structural order. However, extended X-ray absorption fine-structure (EXAFS) studies11 show that each vanadium ion is octahedrally coordinated with six different TCNE molecules, indicating a robust local structural order with a vanadium-nitrogen bond length of 2.084(5) &#197;. Magnetism arises from an antiferromagnetic exchange coupling between the unpaired spins of the TCNE- radical anions, which are distributed across the entire TCNE- molecule , and the spins on the V2+ ions, leading to a local ferrimagnetic ordering with TC ~ 600 K for optimized films5. In addition to exhibiting room temperature magnetic ordering, V[TCNE]x~2 films are semiconducting with 0.5 eV bandgap12. Other properties of note include possible sperimagnetism below a freezing temperature of ~150 K13,14, anomalous positive magnetoresistance12,15,16, and photo-induced magnetism13,17,18.
The CVD method for synthesizing V[TCNE]x~2 thin films is compatible with a variety of substrates due to low temperature (&#60;60 &#176;C) and conformal deposition. Previous studies have shown successful deposition of V[TCNE]x~2 on both rigid and flexible substrates7. Further, this deposition technique lends itself to tuning through modification of precursors and growth parameters.19-22 While the protocol shown here yields the most optimized films to date, significant progress has been made in improving some of the film properties since the discovery of this method and further gains may be possible.

<table><tbody><tr><td colspan="4">&lt;strong&gt;Equipment&lt;/strong&gt;</td></tr><tr><td>Nitrogen Glovebox</td><td>Vacuum Atmospheres</td><td>Omni</td><td>steps done in nitrogen glovebox can also be done in an argon glovebox</td></tr><tr><td>1 L three-neck round bottom flask</td><td>Corning</td><td>4965A-1L</td><td></td></tr><tr><td>500 ml round bottom flask</td><td>Sigma Aldrich</td><td>64678</td><td></td></tr><tr><td>Turbo vacuum pumping station</td><td>Agilent Varian</td><td>G8701A-011-037</td><td></td></tr><tr><td>Glass Stopcock</td><td>Kontes</td><td>185000-2440</td><td></td></tr><tr><td>Glass two way connecting tube</td><td>Corning</td><td>8940-24</td><td>Corning Pyrex(R) 105 degree Angled Tube Adapter with Two-Way 24/40 Standard Taper Joint</td></tr><tr><td>Coldfinger</td><td></td><td></td><td>Custom part made by OSU chemistry glass shop</td></tr><tr><td>Argon Glovebox</td><td>Vacuum Atmospheres</td><td>Nexus I</td><td></td></tr><tr><td>Hot plate stirrer</td><td>Corning</td><td>6795</td><td></td></tr><tr><td>Thermoeletric cooler</td><td>Advanced Thermoelectric</td><td>TCP-50</td><td></td></tr><tr><td>Temperature controller</td><td>Advanced Thermoelectric</td><td>TLZ10</td><td>for TE cooler</td></tr><tr><td>Power supply</td><td>Advanced Thermoelectric</td><td>PS-145W-12V&amp;nbsp;</td><td>for TE cooler and temperature controller</td></tr><tr><td>Temperature controller</td><td>J-Kem&amp;nbsp; Scientific</td><td>Model 150</td><td>For heating coil</td></tr><tr><td>Heating wire</td><td>Pelican Wire Company</td><td>Nichrome 60</td><td></td></tr><tr><td>Custom glassware pieces</td><td></td><td></td><td>Made by OSU Chemistry glass shop</td></tr><tr><td>Vacuum pump</td><td>BOC Edwards</td><td>XDS-5</td><td>Connected to the CVD set-up</td></tr><tr><td>Flow meter</td><td>Gilmont</td><td>GF-2260</td><td></td></tr><tr><td>Micrometer valve</td><td>Gilmont</td><td>7300</td><td>Controls flow of argon over TCNE</td></tr><tr><td>Micrometer valve</td><td>Gilmont</td><td>7100</td><td>Controls flow of argon over&amp;nbsp; V(CO)&lt;sub&gt;6&lt;/sub&gt;</td></tr><tr><td>Tubing</td><td>Tygon</td><td>R3603</td><td>1/8 in walls, connected between valves and meter</td></tr><tr><td>3-way Stopcock</td><td>Nalgene</td><td>6470</td><td>used to adjust the flow rates</td></tr><tr><td>Pressure gauge</td><td>Matheson</td><td>63-4105</td><td>connects to the top of &lt;strong&gt;Figure 1&lt;/strong&gt; part A</td></tr><tr><td>SQUID magnetometer</td><td>Quantum Design</td><td>MPMS-XL</td><td></td></tr><tr><td>EPR</td><td>Bruker</td><td>Elexsys</td><td></td></tr><tr><td>PPMS</td><td>Quantum Design</td><td>14T PPMS</td><td></td></tr><tr><td>Sourcemeter</td><td>Keithely&amp;nbsp;</td><td>2400</td><td></td></tr><tr><td colspan="4">&lt;strong&gt;Materials&lt;/strong&gt;</td></tr><tr><td>Sodium metal</td><td>Sigma Aldrich</td><td>262714</td><td></td></tr><tr><td>Anthracene</td><td>Sigma Aldrich</td><td>141062</td><td></td></tr><tr><td>Anhydrous tetrahydrofuran</td><td>Sigma Aldrich</td><td>186562</td><td></td></tr><tr><td>Vanadium(III) chloride tetrahydrofuran complex</td><td>Sigma Aldrich</td><td>395382</td><td></td></tr><tr><td>Carbon monoxide gas</td><td>OSU stores</td><td>98610</td><td></td></tr><tr><td>Tetraethylammonium bromide</td><td>Sigma Aldrich</td><td>241059</td><td></td></tr><tr><td>Phosphoric acid</td><td>Sigma Aldrich</td><td>79622</td><td></td></tr><tr><td>Methanol</td><td>Sigma Aldrich</td><td>14262</td><td></td></tr><tr><td>Silcone oil</td><td>Sigma Aldrich</td><td>146153</td><td></td></tr><tr><td>Copper pellets</td><td></td><td></td><td>Cut from spare copper wire</td></tr><tr><td>Tetracyanoethylene</td><td>Sigma Aldrich</td><td>T8809</td><td></td></tr><tr><td>Glass slides</td><td>Gold Seal</td><td>3010</td><td></td></tr><tr><td>Activated Charcoal</td><td>Sigma Aldrich</td><td>242276</td><td></td></tr></tbody></table>

chemical vapor deposition of an organic magnet, vanadium tetracyanoethylene

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in traditional materials, including low cost and mechanical flexibility. In a similar vein, it would be advantageous to expand the use of organics into high frequency electronics and spin-based electronics. This work presents a synthetic process for the growth of thin films of the room temperature organic ferrimagnet, vanadium tetracyanoethylene (V[TCNE]x, x~2) by low temperature chemical vapor deposition (CVD). The thin film is grown at &#60;60 &#176;C, and can accommodate a wide variety of substrates including, but not limited to, silicon, glass, Teflon and flexible substrates. The conformal deposition is conducive to pre-patterned and three-dimensional structures as well. Additionally this technique can yield films with thicknesses ranging from 30 nm to several microns. Recent progress in optimization of film growth creates a film whose qualities, such as higher Curie temperature (600 K), improved magnetic homogeneity, and narrow ferromagnetic resonance line-width (1.5 G) show promise for a variety of applications in spintronics and microwave electronics.

The first and easiest method for determining if a deposition is successful is to do a visual inspection of the films. The film should appear dark purple with a mirror finish that is uniform across the substrates. If there are spots on the surface of the substrate where there is no V[TCNE]x~2 or it is lighter in color, then this is likely due to the presence of solvents or other impurities on the substrate surface. Additionally the film should be opaque. Unless a thin film was deposited over a short ti...

Watch this Scientific Journal Video about Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene at JoVE.com

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

We present the synthesis of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x, x~2) via low temperature chemical vapor deposition (CVD). This optimized recipe yields an increase in Curie temperature from 400 K to over 600 K and a dramatic improvement in magnetic resonance properties.

Recent progress in the field of organic materials has yielded devices such as organic light emitting diodes (OLEDs) which have advantages not found in ...

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Research

JoVE Journal

Chemistry

11.4K Views.  The Ohio State University. We present the synthesis of the organic-based ferrimagnet vanadium tetracyanoethylene (V[TCNE]x, x~2) via low temperature chemical vapor deposition (CVD). This optimized recipe yields an increase in Curie temperature from 400 K to over 600 K and a dramatic improvement in magnetic resonance properties.

Video: Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

Fabrication of VB2/Air Cells for Electrochemical Testing

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for synthesizing nanoscopic VB2 is presented as well as step-by-step procedure for applying a zirconium oxide coating to the VB2 particles for stabilization upon discharge. The process for disassembling existing zinc/air cells is shown, in addition construction of the new working electrode to replace the conventional zinc/air cell anode with a the nanoscopic VB2 anode. Finally, discharge of the completed VB2/air battery is reported. We show that using the zinc/air cell as a test bed is useful to provide a consistent configuration to study the performance of the high-energy high capacity nanoscopic VB2 anode.

Fabrication of VB2/Air Cells for Electrochemical Testing

A protocol is presented to study multi-electron metal/air battery systems by using previous technology developed for the zinc/air cell. Electrochemical testing is then performed on fabricated batteries to evaluate performance.

A technique to investigate the properties and performance of new multi-electron metal/air battery systems is proposed and presented. A method for ...

Engineering

Simultaneous Synthesis of Single-walled Carbon Nanotubes and Graphene in a Magnetically-enhanced Arc Plasma

Carbon nanostructures such as single-walled carbon nanotubes (SWCNT) and graphene attract a deluge of interest of scholars nowadays due to their very promising application for molecular sensors, field effect transistor and super thin and flexible electronic devices1-4. Anodic arc discharge supported by the erosion of the anode material is one of the most practical and efficient methods, which can provide specific non-equilibrium processes and a high influx of carbon material to the developing structures at relatively higher temperature, and consequently the as-synthesized products have few structural defects and better crystallinity.
 To further improve the controllability and flexibility of the synthesis of carbon nanostructures in arc discharge, magnetic fields can be applied during the synthesis process according to the strong magnetic responses of arc plasmas. It was demonstrated that the magnetically-enhanced arc discharge can increase the average length of SWCNT 5, narrow the diameter distribution of metallic catalyst particles and carbon nanotubes 6, and change the ratio of metallic and semiconducting carbon nanotubes 7, as well as lead to graphene synthesis 8. 
 Furthermore, it is worthwhile to remark that when we introduce a non-uniform magnetic field with the component normal to the current in arc, the Lorentz force along the J&times;B direction can generate the plasmas jet and make effective delivery of carbon ion particles and heat flux to samples. As a result, large-scale graphene flakes and high-purity single-walled carbon nanotubes were simultaneously generated by such new magnetically-enhanced anodic arc method. Arc imaging, scanning electron microscope (SEM), transmission electron microscope (TEM) and Raman spectroscopy were employed to analyze the characterization of carbon nanostructures. These findings indicate a wide spectrum of opportunities to manipulate with the properties of nanostructures produced in plasmas by means of controlling the arc conditions.

Anodic arc discharge is one of the most practical and efficient methods to synthesize various carbon nanostructures. To increase the arc controllability and flexibility, a non-uniform magnetic field was introduced to process the one-step synthesis of large-scale graphene flakes and high-purity single-walled carbon nanotubes.

Carbon nanostructures such as single-walled carbon nanotubes (SWCNT) and graphene attract a deluge of interest of scholars nowadays due to their very ...

Bioengineering

Reverse Microemulsion-mediated Synthesis of Monometallic and Bimetallic Early Transition Metal Carbide and Nitride Nanoparticles

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The silica-encapsulated metal oxide nanoparticles are then carburized in a methane/hydrogen atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal carbide nanoparticles. During the carburization process, the silica shells prevent the sintering of adjacent carbide nanoparticles while also preventing the deposition of excess surface carbon. Alternatively, the silica-encapsulated metal oxide nanoparticles can be nitridized in an ammonia atmosphere at temperatures over 800 &#176;C to form silica-encapsulated early transition metal nitride nanoparticles. By adjusting the reverse microemulsion parameters, the thickness of the silica shells, and the carburization/nitridation conditions, the transition metal carbide or nitride nanoparticles can be tuned to various sizes, compositions, and crystal phases. After carburization or nitridation, the silica shells are then removed using either a room-temperature aqueous ammonium bifluoride solution or a 0.1 to 0.5 M NaOH solution at 40-60 &#176;C. While the silica shells are dissolving, a high surface area support, such as carbon black, can be added to these solutions to obtain supported early transition metal carbide or nitride nanoparticles. If no high surface area support is added, then the nanoparticles can be stored as a nanodispersion or centrifuged to obtain a nanopowder.

A &#8220;removable ceramic coating method&#8221; is presented in visual format for the synthesis of non-sintered and metal-terminated monometallic and bimetallic early transition metal carbide and nitride nanoparticles with tunable sizes and crystal structures.

A reverse microemulsion is used to encapsulate monometallic or bimetallic early transition metal oxide nanoparticles in microporous silica shells. The ...

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. Conventionally reserved for the fabrication of metal thin films, thermal evaporation deposits bismuth into an array of vertical single crystalline nanowires over a flat thin film of vanadium held at RT, which is freshly deposited by magnetron sputtering or thermal evaporation. By controlling the temperature of the growth substrate the length and width of the nanowires can be tuned over a wide range. Responsible for this novel technique is a previously unknown nanowire growth mechanism that roots in the mild porosity of the vanadium thin film. Infiltrated into the vanadium pores, the bismuth domains (~ 1 nm) carry excessive surface energy that suppresses their melting point and continuously expels them out of the vanadium matrix to form nanowires. This discovery demonstrates the feasibility of scalable vapor phase synthesis of high purity nanomaterials without using any catalysts.

A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented.

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. ...

Aerosol-assisted Chemical Vapor Deposition of Metal Oxide Structures: Zinc Oxide Rods

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, their high cost production and/or incompatibility with microfabrication technologies, due to the use of pre-deposited catalyst-seeds and/or high processing temperatures exceeding 900 &#176;C, represent a drawback for a widespread use of these methods. Here, however, we report the synthesis of ZnO rods via a non-catalyzed vapor-solid mechanism enabled by using an aerosol-assisted chemical vapor deposition (CVD) method at 400 &#176;C with zinc chloride (ZnCl2) as the precursor and ethanol as the carrier solvent. This method provides both single-step formation of ZnO rods and the possibility of their direct integration with various substrate types, including silicon, silicon-based micromachined platforms, quartz, or high heat resistant polymers. This potentially facilitates the use of this method at a large-scale, due to its compatibility with state-of-the-art microfabrication processes for device manufacture. This report also describes the properties of these structures (e.g., morphology, crystalline phase, optical band gap, chemical composition, electrical resistance) and validates its gas sensing functionality towards carbon monoxide.

Columnar zinc oxide structures in the form of rods are synthesized via aerosol-assisted chemical vapor deposition without the use of pre-deposited catalyst-seed particles. This method is scalable and compatible with various substrates based on either silicon, quartz or polymers.

Whilst columnar zinc oxide (ZnO) structures in the form of rods or wires have been synthesized previously by different liquid- or vapor-phase routes, ...

Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. Conductive polymers, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT), and a semiconducting polymer, poly(thieno[3,2-b]thiophene) (PTT), were deposited on unconventional highly-disordered and textured substrates with high surface areas, such as paper, towels and fabrics. This reported deposition chamber is an improvement of previous vapor reactors because our system can accommodate both volatile and nonvolatile monomers, such as 3,4-propylenedioxythiophene and thieno[3,2-b]thiophene. Utilization of both solid and liquid oxidants are also demonstrated. One limitation of this method is that it lacks sophisticated in situ thickness monitors. Polymer coatings made by the commonly used solution-based coating methods, such as spin-coating and surface grafting, are often not uniform or susceptible to mechanical degradation. This reported vapor phase deposition method overcomes those drawbacks and is a strong alternative to common solution-based coating methods. Notably, polymer films coated by the reported method are uniform and conformal on rough surfaces, even at a micrometer scale. This feature allows for future application of vapor deposited polymers in electronics devices on flexible and highly textured substrates.

This paper presents a protocol for reactive vapor deposition of poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), and poly(thieno[3,2-b]thiophene) films on glass slides and rough substrates, such as textiles and paper.

We demonstrate a method of conformally coating conjugated polymers on arbitrary substrates using a custom-designed, low-pressure reaction chamber. ...

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We present methods for depositing and passively manipulating C60 molecules on rippled graphene that advance the pursuit of realizing applications involving 1D C60/graphene hybrid structures. The techniques applied in this exposition are geared towards high vacuum systems with preparation areas capable of supporting molecular deposition as well as thermal annealing of the samples. We focus on C60 deposition at low pressure using a homemade Knudsen cell connected to a scanning tunneling microscopy (STM) system. The number of molecules deposited is regulated by controlling the temperature of the Knudsen cell and the deposition time. One-dimensional (1D) C60 chain structures with widths of two to three molecules can be prepared via tuning of the experimental conditions. The surface mobility of the C60 molecules increases with annealing temperature allowing them to move within the periodic potential of the rippled graphene. Using this mechanism, it is possible to control the transition of 1D C60 chain structures to a hexagonal close packed quasi-1D stripe structure.

Preparation and Characterization of C60/Graphene Hybrid Nanostructures

Here we present a protocol for the fabrication of C60/graphene hybrid nanostructures by physical thermal evaporation. Particularly, the proper manipulation of deposition and annealing conditions allow the control over the creation of 1D and quasi 1D C60 structures on rippled graphene.

Physical thermal deposition in a high vacuum environment is a clean and controllable method for fabricating novel molecular nanostructures on graphene. We ...

Atomic Layer Deposition of Vanadium Dioxide and a Temperature-dependent Optical Model

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with wafer-scale uniformity and angstrom level control of thickness, the method of atomic-layer deposition was chosen. This ALD process enables high-quality, low-temperature (&#8804;150 &#176;C) growth of ultrathin films (100-1000 &#197;) of VO2. For this demonstration, the VO2 films were grown on sapphire substrates. This low temperature growth technique produces mostly amorphous VO2 films. A subsequent anneal in an ultra-high vacuum chamber with a pressure of 7x10-4 Pa of ultra-high purity (99.999%) oxygen produced oriented, polycrystalline VO2 films. The crystallinity, phase, and strain of the VO2 were determined by Raman spectroscopy and X-ray diffraction, while the stoichiometry and impurity levels were determined by X-ray photoelectron spectroscopy, and finally the morphology was determined by atomic force microscopy. These data demonstrate the high-quality of the films grown by this technique. A model was created to fit to the data for VO2 in its metallic and insulating phases in the near infrared spectral region. The permittivity and refractive index of the ALD VO2 agreed well with the other fabrication methods in its insulating phase, but showed a difference in its metallic state. Finally, the analysis of the films&#39; optical properties enabled the creation of a wavelength- and temperature-dependent model of the complex optical refractive index for developing VO2 as a tunable refractive index material.

Thin films (100-1000 &#197;) of vanadium dioxide (VO2) were created by atomic-layer deposition (ALD) on sapphire substrates. Following this, the optical properties were characterized through the metal-insulator transition of VO2. From the measured optical properties, a model was created to describe the tunable refractive index of VO2.

Vanadium dioxide is a material that has a reversible metal-insulator phase change near 68 &#176;C. To grow VO2 on a wide variety of substrates, with ...

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

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

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

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

Deposition of Bi2Te3 and Sb2Te3 Thin Films on Glass Substrates via RF Sputtering

Fabrication of Bi2Te3 and Sb2Te3 Thermoelectric Thin Films using Radio Frequency Magnetron Sputtering Technique

Through various studies on thermoelectric (TE) materials, thin film configuration gives superior advantages over conventional bulk TEs, including adaptability to curved and flexible substrates. Several different thin film deposition methods have been explored, yet magnetron sputtering is still favorable due to its high deposition efficiency and scalability. Therefore, this study aims to fabricate a bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) thin film via the radio frequency (RF) magnetron sputtering method. The thin films were deposited on soda lime glass substrates at ambient temperature. The substrates were first washed using water and soap, ultrasonically cleaned with methanol, acetone, ethanol, and deionized water for 10 min, dried with nitrogen gas and hot plate, and finally treated under UV ozone for 10 min to remove residues before the coating process. A sputter target of Bi2Te3 and Sb2Te3 with Argon gas was used, and pre-sputtering was done to clean the target&#39;s surface. Then, a few clean substrates were loaded into the sputtering chamber, and the chamber was vacuumed until the pressure reached 2 x 10-5 Torr. The thin films were deposited for 60 min with Argon flow of 4 sccm and RF power at 75 W and 30 W for Bi2Te3 and Sb2Te3, respectively. This method resulted in highly uniform n-type Bi2Te3 and p-type Sb2Te3 thin films.

Author Spotlight: Advancements in High-Performance Thermoelectric Thin Films Through Radio Frequency Magnetron Sputtering

The manuscript describes a protocol for radio frequency magnetron sputtering of Bi2Te3 and Sb2Te3 thermoelectric thin films on glass substrates, which represents a reliable deposition method that provides a wide range of applications with the potential for further development.

Chemical Vapor Deposition of an Organic Magnet, Vanadium Tetracyanoethylene

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