This work was supported by the Wake Forest Chemistry Department and the Wake Forest Center for Energy, Environment, and Sustainability (CEES). We thank Charles Mooney and the Analytical Instrumentation Facility of the North Carolina State University for assistance with SEM imaging.

1. Preparing Xerogel Pellets
<ol>
	<li>Gel Synthesis
	<ol>
		<li>Add a 25 mm magnetic stir bar and 113 mL of deionized water to a 500 mL beaker. Magnetically stir the deionized water at the highest rate that does not form a vortex.</li>
		<li>Slowly add 13.05 g (0.056 mol) of anhydrous zirconium chloride to the deionized water in small increments. After all of the anhydrous zirconium chloride has dissolved, add 53.29 g (0.296 mol) of glucose to the solution.</li>
		<li>After all of the glucose has dissolved in the solution, add 3.73 g (0.01 mol) of yttrium nitrate hexahydrate to the solution. Increase the rate of magnetic stirring to ~700 rpm and wait for all of the yttrium nitrate hexahydrate to dissolve in solution.</li>
		<li>Add 42 mL of propylene oxide to the solution. Continue stirring at ~700 rpm for the propylene oxide to mix with the aqueous solution. Once the propylene oxide is mixed with the aqueous solution (~10 s), decrease the magnetic stirring to ~150 rpm.</li>
		<li>Continue stirring until the magnetic stir bar has stopped moving due to formation of the gel. The gel typically forms within 3 min. 
		NOTES: Adding anhydrous zirconium chloride to deionized water is a highly exothermic reaction and the anhydrous zirconium chloride will plume if it is added too quickly. 
		The formulation provided in Section 1.1. corresponds to a glucose to total metals (zirconium + yttrium) molar ratio of 4.5:1. The representative results section includes data for glucose to total metals molar ratios of 0:1, 2.25:1, and 4.5:1. The amount of glucose in the formulation is only limited by the solubility of glucose in the solution. For reference, the maximum solubility of glucose in water at 20 &#176;C is 47.8 wt%.15</li>
	</ol>
	</li>
	<li>Aging and Washing the Gel
	<ol>
		<li>Tightly cover the beaker containing the gel with Parafilm and let it age for 24 h by leaving the covered beaker at room temperature.</li>
		<li>Remove the cover from the beaker and decant the liquid on top of the gel.</li>
		<li>Add 300 mL of absolute ethanol to the beaker containing the gel, tightly cover the beaker with Parafilm, and leave the covered beaker at room temperature for 24 h.</li>
		<li>Repeat step 1.2.3 two more times for a total of three ethanol washings over a total period of 72 h.</li>
	</ol>
	</li>
	<li>Drying the Gel into a Xerogel
	<ol>
		<li>Remove the gel from the beaker and place it in a 2 L porcelain evaporating dish (24 cm outside top diameter) using a laboratory spatula.</li>
		<li>Break the gel into approximately 1 cm x 1 cm pieces with a spatula and spread out the pieces over the surface of the evaporating dish.</li>
		<li>Let the gel pieces dry under ambient conditions for one week or until the gel is dry. The gel is considered dry when it can be ground into a fine powder.</li>
		<li>Grind all of the xerogel into a fine powder with a mortar and pestle. 
		NOTE: Once the gel is dry, it is considered a xerogel because it was dried under ambient conditions.</li>
	</ol>
	</li>
	<li>Pressing the Xerogel into a Pellet
	<ol>
		<li>Place 1 g of xerogel powder into a cylindrical pellet press die with a diameter of 13 mm.</li>
		<li>Using a hydraulic press, apply 22 kN of force for 90 s to press the xerogel gel into a pellet.</li>
		<li>Slowly release the force applied by the press. Slowly eject the pellet out of the pellet die and then carefully remove the pellet.</li>
	</ol>
	</li>
</ol>
2. Sintering the Xerogel Pellet in an Inert Atmosphere
<ol>
	<li>Place the xerogel pellet onto an alumina or yttria-stabilized zirconia plate and load the plate into the center of a tube furnace.</li>
	<li>Flow argon at a rate of one third the volume of the working tube per minute. This corresponds to an argon flow rate of 750 mL&#183;min-1 for the working tube used in this work. Vent the gas outlet to a fume hood.</li>
	<li>Flow argon for at least 15 min before starting to heat the tube furnace.</li>
	<li>While continuously flowing argon at a constant rate, program the tube furnace temperature controller to the following heating schedule:
	<ol>
		<li>Hold at room temperature for 15 min.</li>
		<li>Heat to 850 &#176;C at a ramp rate of 5 &#176;C&#183;min-1.</li>
		<li>Heat to desired sintering temperature at a ramp rate of 2 &#176;C&#183;min-1.</li>
		<li>Hold at the desired sintering temperature for 2 h.</li>
		<li>Cool to 850 &#176;C at a ramp rate of 2 &#176;C&#183;min-1.</li>
		<li>Cool to room temperature at a ramp rate of 5 &#176;C&#183;min-1.</li>
	</ol>
	</li>
	<li>Start the program and double-check that the tube furnace is heating up following the schedule provided in section 2.3.</li>
	<li>Remove pellet from the tube furnace after the heating program has completed.</li>
</ol>
3. Determining Carbon Template Concentration
<ol>
	<li>Cut a ~50 mg piece out of the sintered xerogel pellet with a utility knife and grind it into a fine powder with an agate mortar and pestle.</li>
	<li>Place ~50 mg of the fine powder into an alumina sample cup for thermogravimetric analysis.</li>
	<li>Using a thermogravimetric analyzer (TGA), heat the sample at a rate of 10 &#176;C&#183;min-1 from ambient temperature to 1,200 &#176;C while flowing air over the sample at a rate of 100 mL&#183;min-1.</li>
	<li>Calculate the percent change in weight that occurs between ~350 &#176;C and ~700 &#176;C. This weight percent corresponds to the total carbon content in the sample. 
	NOTE: If a weight increase occurs in the 350 &#176;C to 700 &#176;C range, a carbide phase has formed and the calculation of carbon content is more complex. For this case, please refer to calculations described in the literature.14 Carbon elemental analysis has been used to confirm that carbon content can be calculated from TGA measurements.</li>
</ol>
4. Preparing High Surface Area YSZ Scaffold by Carbon Template Removal
<ol>
	<li>Place the sintered xerogel pellet in an alumina crucible.</li>
	<li>Place the crucible into a box furnace at 700 &#176;C for 2 h.</li>
	<li>Carefully remove the hot crucible from the box furnace with stainless steel crucible tongs and allow it to cool to room temperature for one hour before removing the porous, white YSZ scaffold.</li>
</ol>

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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+highly+conductive+oxide+anode+for+solid+oxide+fuel+cells.">A highly conductive oxide anode for solid oxide fuel cells.</a> Electrochem. Solid-State Lett. 14 (1), B1-B5 (2011).</li><li>Vo, N. M., Gross, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+vanadium+deficiency+on+the+stability+of+Pd+and+Pt+catalysts+in+lanthanum+strontium+vanadate+solid+oxide+fuel+cell+anodes.">The effect of vanadium deficiency on the stability of Pd and Pt catalysts in lanthanum strontium vanadate solid oxide fuel cell anodes.</a> J. Electrochem. Soc. 159 (5), B641-B646 (2012).</li><li>Sholklapper, T. Z., Jacobson, C. P., Visco, S. J., De Jonghe, L. 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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=La-doped+SrTiO3+as+anode+material+for+IT-SOFC.">La-doped SrTiO3 as anode material for IT-SOFC.</a> Solid State Ionics. 192 (1), 491-493 (2011).</li><li>Choi, S., Shin, J., Kim, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+electrochemical+and+thermodynamic+characterization+of+PrBaCo2-xFexO5+&#948;+(x=0,0.5,1)+infiltrated+into+yttria-stabilized+zirconia+scaffold+as+cathodes+for+solid+oxide+fuel+cells.">The electrochemical and thermodynamic characterization of PrBaCo2-xFexO5+&#948; (x=0,0.5,1) infiltrated into yttria-stabilized zirconia scaffold as cathodes for solid oxide fuel cells.</a> J. Power Sources. 201, 10-17 (2012).</li><li>Kungas, R., Kim, J. S., Vohs, J. M., Gorte, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Restructuring+porous+YSZ+by+treatment+in+hydrofluoric+acid+for+use+in+SOFC+cathodes.">Restructuring porous YSZ by treatment in hydrofluoric acid for use in SOFC cathodes.</a> J. Am. Ceram. Soc. 94 (7), 2220-2224 (2011).</li><li>Jung, W., Dereux, J. O., Chueh, W. C., Hao, Y., Haile, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+electrode+activity+of+nanostructured,+columnar+ceria+films+for+solid+oxide+fuel+cells.">High electrode activity of nanostructured, columnar ceria films for solid oxide fuel cells.</a> Energy Environ. Sci. 5, 8682-8689 (2012).</li><li>Cottam, M., Muhoza, S., Gross, M. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preserving+nanomorphology+in+YSZ+scaffolds+at+high+temperatures+via+in+situ+carbon+templating+of+hybrid+materials.">Preserving nanomorphology in YSZ scaffolds at high temperatures via in situ carbon templating of hybrid materials.</a> J. Amer. Ceram. Soc. 99 (8), 2625-2631 (2016).</li><li>Alves, L. A., Silva, J. B. A., Giulietti, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solubility+of+D-Glucose+in+Water+and+Ethanol/Water+Mixtures.">Solubility of D-Glucose in Water and Ethanol/Water Mixtures.</a> J. Chem. Eng. Data. 52, 2166-2170 (2007).</li><li>Thommes, M., Smarsly, B., Groenewolt, M., Ravikovitch, P. I., Neimark, A. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Adsorption+hysteresis+of+nitrogen+and+argon+in+pore+networks+and+characterization+of+novel+micro-+and+mesoporous+silicas.">Adsorption hysteresis of nitrogen and argon in pore networks and characterization of novel micro- and mesoporous silicas.</a> Langmuir. 22, 756-764 (2006).</li><li>Chervin, C. N., 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=A+non-alkoxide+sol-gel+method+for+the+preparation+of+homogeneous+nanocrystalline+powders+of+La0.85Sr0.15MnO3.">A non-alkoxide sol-gel method for the preparation of homogeneous nanocrystalline powders of La0.85Sr0.15MnO3.</a> Chem. Mater. 18, 1928-1937 (2006).</li><li>Clapsaddle, B. J., Sprehn, D. W., Gash, A. E., Satcher, J. H., Simpson, R. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+versatile+sol-gel+synthesis+route+to+metal-silicon+mixed+oxide+nanocomposites+that+contain+metal+oxides+as+a+major+phase.">A versatile sol-gel synthesis route to metal-silicon mixed oxide nanocomposites that contain metal oxides as a major phase.</a> J. Non-Crystalline Solids. 350, 173-181 (2004).</li><li>Gash, A. E., 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=Use+of+epoxides+in+the+sol-gel+synthesis+of+porous+iron+(III)+oxide+monoliths+from+Fe(III)+salts.">Use of epoxides in the sol-gel synthesis of porous iron (III) oxide monoliths from Fe(III) salts.</a> Chem. Mater. 13, 999-1007 (2001).</li></ol>

We have nothing to disclose.

With this in situ carbon templating approach, one can create and preserve nanomorphology in mixed-metal-oxides at traditional ceramic scaffold sintering temperatures. The resulting surface areas are up to 80 times higher than traditionally sintered scaffolds and up to 4 times higher than scaffolds fabricated by complex deposition techniques.14 The propylene oxide-glucose gel system is highly flexible for tuning the concentration of the carbon template, allowing one to systematically control the carbon template concentration between 10 vol% carbon and virtually 100 vol% carbon.
There are three critical steps to the procedure. First, the propylene oxide must be well mixed with the aqueous solution to form the gel (Step 1.1.4). This is accomplished by stirring at ~700 rpm while the propylene oxide is added. If the solution is not stirred turbulently, the propylene oxide will form a separate layer above the aqueous solution and the gel will not form. Second, the working tube must be flushed with argon before heating the tube furnace for sintering (Step 2.2). This is accomplished by flowing argon for 15 min at a rate of one third the volume of the working tube per minute. In addition, the working tube must be leak tight to prevent air from entering the working tube during sintering. Oxygen from the air will destroy the carbon template by oxidation of carbon to carbon dioxide. Third, the sintering ramp rate from 850 &#176;C to sintering temperature should not exceed 2 &#176;C&#183;min-1. A faster ramp rate could cause the scaffold to fracture.
The majority of possible carbon template concentrations will result in a monolithic scaffold. Obviously, there is a critical carbon concentration threshold at which a monolithic scaffold will not form because the YSZ particles would be disconnected from each other. However, this scenario also has utility. One could load a traditional low surface area scaffold with a high carbon concentration gel and carry out the same inert sintering procedure described here. The result would be YSZ nanoparticles decorated onto the scaffold surface in a nanoparticle concentration controlled by the glucose concentration in the gel formulation.
Propylene oxide gel syntheses have been reported for a large number of metals in the literature.17,18,19 In addition, the propylene oxide gel synthesis can accommodate multiple metals in essentially any mixed-metal composition that is desired. While the motivation for this work was driven by solid oxide fuel cell electrode needs, the approach is applicable for a wide range of mixed-metal-oxides for a wide range of applications.
It is important to recognize that if the sintering temperature is high enough, metal-carbide phases will form, rather than the oxide. The temperature at which this happens depends on the specific metals one is using. For YSZ, we have found that a zirconium carbide phase begins to form around 1,150 &#176;C and nearly all of the zirconium is in the form of zirconium carbide by 1,400 &#176;C.14 For sintering temperatures below 1,300 &#176;C, all of the zirconium reverts back to the YSZ phase upon carbon template removal by oxidation. For sintering temperatures above 1,300 &#176;C, we observe small amounts of a monoclinic zirconium oxide phase. It is likely that above 1,300 &#176;C, some zirconium carbide particles are sufficiently separated from yttrium such that heating in air to 700 &#176;C is not enough thermal energy for complete dissolution of zirconium back into YSZ. Our group is currently considering alternative sintering environments to mitigate carbide formation while preserving the carbon template during sintering.
In summary, the propylene oxide-glucose gel system has outstanding flexibility in specifying the inorganic:organic ratio, the type of metals, and the mixed-metal composition for realizing high surface area mixed-metal-oxide nanomorphologies at high temperatures.

The solid oxide fuel cell (SOFC) holds great promise as an alternative energy conversion technology for the efficient generation of clean electrical power.1 Considerable progress has been made in the research and development of this technology; however, improvements in electrode performance are still needed to achieve reliable commercialization. The electrode often comprises a porous ceramic scaffold with electrocatalytic particles decorated on the scaffold surface. A large body of research has focused on increasing the surface area of the electrocatalytic particles to increase performance,2,3,4,5,6,7,8 but there is very little research on increasing the scaffold surface area. Increasing the scaffold surface area is challenging because they are sintered at high temperatures, 1,100 &#176;C to 1,500 &#176;C.
Scaffolds processed by traditional sintering typically have a specific surface area of 0.1-1 m2&#183;g-1.8,9,10,11 There are a few reports on increasing the scaffold surface area. In one case, the surface area of a traditionally sintered scaffold was enhanced by dissolution and precipitation of the scaffold surface using hydrofluoric acid, achieving a specific surface area of 2 m2&#183;g-1.12 In another, high temperatures were avoided altogether by using pulsed laser deposition, achieving a specific surface area of 20 m2&#183;g-1.13 The rationale behind the development of our technique was to create a low cost fabrication process that provides unprecedented scaffold surface areas and uses traditional sintering temperatures so that the process can be adopted easily. With the technique reported here, scaffold surface areas up to 80 m2&#183;g-1 have been demonstrated while being processed at traditional sintering temperatures.14
Our research is primarily motivated by SOFC electrode engineering, but the technique is more broadly applicable to other fields and applications. Generally, the in situ carbon templating method is a flexible approach that can produce nanostructured, high surface area mixed-metal ceramic materials in the powder or porous scaffold form. It is flexible in that the mixed-metal ceramic composition, surface area, porosity, and pore size can all be tuned systematically. High temperatures are often needed to form the desired phase in mixed-metal ceramics, and this approach preserves ceramic nanomorphology while allowing one to choose essentially any processing temperature.
This method involves the synthesis of a hybrid inorganic-organic propylene-oxide-based gel, with a well define stoichiometry of metal ions and ratio of inorganic to organic content. The gel is dried under ambient conditions to form a xerogel. The xerogel is sintered in an argon atmosphere at the desired temperature. Upon heating, the organic component decomposes leaving behind a carbon template in situ, which remains for the duration of sintering. The carbon template is subsequently removed by low temperature oxidation in air, resulting in a nanostructured, high surface area ceramic.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Zirconium (IV) chloride, 99.5+%</td>
			<td>Alfa Aesar</td>
			<td>12104</td>
			<td>Air sensitive</td>
		</tr>
		<tr>
			<td>Yttium (III) nitrate hexadydrate, 99.9%</td>
			<td>Alfa Aesar</td>
			<td>12898</td>
			<td>Oxidizer</td>
		</tr>
		<tr>
			<td>D+ Glucose Anhydrous, &#8805; 99.5%</td>
			<td>US Biological Life Sciences</td>
			<td>G3050</td>
			<td></td>
		</tr>
		<tr>
			<td>(&#177;)-Propylene Oxide, &#8805; 99%</td>
			<td>Sigma Aldrich</td>
			<td>110205</td>
			<td>Extremely flammable</td>
		</tr>
		<tr>
			<td>Ethanol 200 Proof</td>
			<td>Decon Laboratories, Inc.</td>
			<td>2716GEA</td>
			<td></td>
		</tr>
		<tr>
			<td>Argon, (99.997%)</td>
			<td>Airgas</td>
			<td>AR 300</td>
			<td>Industrial grade</td>
		</tr>
	</tbody>
</table>

high temperature fabrication of nanostructured yttria-stabilized-zirconia (ysz) scaffolds by in situ carbon templating xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

Phase purity was confirmed by X-ray diffraction (XRD) as previously reported by Cottam et al.14 YSZ scaffold specific surface area as a function of carbon template concentration is shown in Figure 1. The concentration is shown as the volume percent of total solids in the sintered xerogel pellet. The carbon template concentration systematically increases with increasing glucose concentration in the gel formulation. As shown in Figure 1, the specific surface area systematically increases from 10 m2&#183;g-1 to 68 m2&#183;g-1 by increasing the glucose:metals molar ratio from 0:1 to 4.5:1.
The carbon template concentration was quantified using TGA (Figure 2). The carbon template concentration was 4 wt% and 64 wt% of total solids for glucose:metals molar ratios of 0:1 and 4.5:1. A YSZ density of 5.9 g&#183;cm3 and a carbon density of 2.15 g&#183;cm3 were used to convert between weight percent and volume percent.
Figure 3 shows scanning electron microscopy (SEM) images of the YSZ xerogel with and without the glucose additive. Both samples were similarly sintered at 1,150 &#176;C in argon and burned out in air at 700 &#176;C. The particles of YSZ xerogel with glucose additive are several times smaller than those without glucose additive. The formation of smaller particles by adding glucose to the gel is consistent with their high carbon content and surface area.
Figure 4 shows XRD patterns of the strongest YSZ peak for YSZ scaffolds as a function of glucose:metals molar ratio. The crystallite size was calculated using these peaks and the Scherrer equation. The crystallite size decreased from 22 nm to 12 nm to 9 nm as the glucose:metals molar ratio was increased from 0:1 to 2.25:1 to 4.5:1. The crystallite size progression is consistent with the observed increase in surface area with increasing glucose:metals molar ratio.
Figure 5 shows the YSZ scaffold pore size distribution as a function of glucose:metals molar ratio. The adsorption/desorption data was collected with a physical adsorption instrument, which is limited to calculating pore sizes between 2 nm and 14 nm. The pore size distribution calculated from N2 adsorption data is shown in Figure 5a. Only the 2.25:1 glucose:metals molar ratio data shows a maximum. Since the instrumentation was limited to detecting 14 nm pores, pore size distributions from N2 desorption data were also calculated, Figure 5b. Desorption data tends to show &#34;artificially&#34; narrow pore size distributions and &#34;artificially&#34; smaller pores16; however, the desorption data provides more insight into the progression of pore size distribution than the adsorption data. The differences in pore size distribution for adsorption and desorption data is best compared for the 2.25:1 glucose:metals data in Figure 5. The peak of the pore size distribution shifts from 10 nm to 7 nm and the distribution is narrower. Extrapolating to the 4.5:1 data, it seems reasonable to assume the peak of the pore size distribution is in the 16-20 nm range. Overall, Figure 5 shows both the number of pores and size of pores increase with an increase in glucose:metals molar ratio.
<img alt="Figure 1" src="/files/ftp_upload/55500/55500fig1.jpg" /> 
Figure 1: YSZ scaffold surface area as a function of carbon template concentration and glucose:metals molar ratio. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55500/55500fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55500/55500fig2.jpg" /> 
Figure 2: TGA curves in flowing air for xerogels with glucose:metal molar ratios of 0:1 and 4.5:1 sintered at 1,150 &#176;C in argon for 2 h. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55500/55500fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55500/55500fig3.jpg" /> 
Figure 3: SEM micrographs of YSZ scaffolds for glucose:metals molar ratios of (a) 4.5:1 and (b) 0:1. The xerogels were sintered in argon at 1,150 &#176;C for 2 h and then heated in air at 700 &#176;C. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55500/55500fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55500/55500fig4.jpg" /> 
Figure 4: XRD of strongest YSZ peak for YSZ scaffolds as a function of glucose:metals molar ratio. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55500/55500fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/55500/55500fig5.jpg" /> 
Figure 5: YSZ scaffold Dollimore-Heal pore size distribution as a function of glucose:metals molar ratio calculated from (a) N2 adsorption data and (b) N2 desorption data. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55500/55500fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels at JoVE.com

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

high-temperature-fabrication-nanostructured-yttria-stabilized

Nanyang Technological University

Research

JoVE Journal

Engineering

10.5K Views.  Wake Forest University. A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 °C and 1,400 °C is presented.

Video: High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

Fabrication of Silica Ultra High Quality Factor Microresonators

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the quality factor (Q) of the cavity, can be in excess of 500ns for cavities with Q factors above 100 million. As a result of their low material losses, silica microcavities have demonstrated some of the longest photon lifetimes to date1-2. Since a portion of the circulating light extends outside the resonator, these devices can also be used to probe the surroundings. This interaction has enabled numerous experiments in biology, such as single molecule biodetection and antibody-antigen kinetics, as well as discoveries in other fields, such as development of ultra-low-threshold microlasers, characterization of thin films, and cavity quantum electrodynamics studies.3-7
The two primary silica resonant cavity geometries are the microsphere and the microtoroid. Both devices rely on a carbon dioxide laser reflow step to achieve their ultra-high-Q factors (Q&gt;100 million).1-2,8-9 However, there are several notable differences between the two structures. Silica microspheres are free-standing, supported by a single optical fiber, whereas silica microtoroids can be fabricated on a silicon wafer in large arrays using a combination of lithography and etching steps. These differences influence which device is optimal for a given experiment.
Here, we present detailed fabrication protocols for both types of resonant cavities. While the fabrication of microsphere resonant cavities is fairly straightforward, the fabrication of microtoroid resonant cavities requires additional specialized equipment and facilities (cleanroom). Therefore, this additional requirement may also influence which device is selected for a given experiment.
Introduction
An optical resonator efficiently confines light at specific wavelengths, known as the resonant wavelengths of the device. 1-2 The common figure of merit for these optical resonators is the quality factor or Q. This term describes the photon lifetime (&tau;o) within the resonator, which is directly related to the resonator's optical losses. Therefore, an optical resonator with a high Q factor has low optical losses, long photon lifetimes, and very low photon decay rates (1/&tau;o). As a result of the long photon lifetimes, it is possible to build-up extremely large circulating optical field intensities in these devices. This very unique property has allowed these devices to be used as laser sources and integrated biosensors.10
A unique sub-class of resonators is the whispering gallery mode optical microcavity. In these devices, the light is confined in circular orbits at the periphery. Therefore, the field is not completely confined within the device, but evanesces into the environment. Whispering gallery mode optical cavities have demonstrated some of the highest quality factors of any optical resonant cavity to date.9,11 Therefore, these devices are used throughout science and engineering, including in fundamental physics studies and in telecommunications as well as in biodetection experiments. 3-7,12
Optical microcavities can be fabricated from a wide range of materials and in a wide variety of geometries. A few examples include silica and silicon microtoroids, silicon, silicon nitride, and silica microdisks, micropillars, and silica and polymer microrings.13-17 The range in quality factor (Q) varies as dramatically as the geometry. Although both geometry and high Q are important considerations in any field, in many applications, there is far greater leverage in boosting device performance through Q enhancement. Among the numerous options detailed previously, the silica microsphere and the silica microtoroid resonator have achieved some of the highest Q factors to date.1,9 Additionally, as a result of the extremely low optical loss of silica from the visible through the near-IR, both microspheres and microtoroids are able to maintain their Q factors over a wide range of testing wavelengths.18 Finally, because silica is inherently biocompatible, it is routinely used in biodetection experiments.
In addition to high material absorption, there are several other potential loss mechanisms, including surface roughness, radiation loss, and contamination loss.2 Through an optimization of the device size, it is possible to eliminate radiation losses, which arise from poor optical field confinement within the device. Similarly, by storing a device in an appropriately clean environment, contamination of the surface can be minimized. Therefore, in addition to material loss, surface scattering is the primary loss mechanism of concern.2,8
In silica devices, surface scattering is minimized by using a laser reflow technique, which melts the silica through surface tension induced reflow. While spherical optical resonators have been studied for many years, it is only with recent advances in fabrication technologies that researchers been able to fabricate high quality silica optical toroidal microresonators (Q&gt;100 million) on a silicon substrate, thus paving the way for integration with microfluidics.1
The present series of protocols details how to fabricate both silica microsphere and microtoroid resonant cavities. While silica microsphere resonant cavities are well-established, microtoroid resonant cavities were only recently invented.1 As many of the fundamental methods used to fabricate the microsphere are also used in the more complex microtoroid fabrication procedure, by including both in a single protocol it will enable researchers to more easily trouble-shoot their experiments.

We describe the use of a carbon dioxide laser reflow technique to fabricate silica resonant cavities, including free-standing microspheres and on-chip microtoroids. The reflow method removes surface imperfections, allowing long photon lifetimes within both devices. The resulting devices have ultra high quality factors, enabling applications ranging from telecommunications to biodetection.

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the ...

Preparation and Reactivity of Gasless Nanostructured Energetic Materials

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+C). The structural transformations of reactive media, which take place during HEBM, define the reaction mechanism in the produced energetic&#160;composites. Varying the processing conditions permits fine tuning of the milling-induced microstructures of the fabricated composite particles. In turn, the reactivity, i.e., self-ignition temperature, ignition delay time, as well as reaction kinetics, of high energy density materials depends on its microstructure. Analysis of the milling-induced microstructures suggests that the formation of fresh oxygen-free intimate high surface area contacts between the reagents is responsible for the enhancement of their reactivity. This manifests itself in a reduction of ignition temperature and delay time, an increased rate of chemical reaction, and an overall decrease of the effective activation energy of the reaction. The protocol provides a detailed description for the preparation of reactive nanocomposites with tailored microstructure using short-term HEBM method. It also describes a high-speed thermal imaging technique to determine the ignition/combustion characteristics of the energetic materials. The protocol can be adapted to preparation and characterization of a variety of nanostructured energetic composites.

This protocol describes the preparation of gasless nanostructured energetic materials (Ni+Al, Ta+C, Ti+C) using the short-term high-energy ball milling (HEBM) technique. It also describes a high-speed thermal imaging method to study the reactivity of mechanically fabricated nanocomposites. These protocols can be extended to other reactive nanostructured energetic materials.

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the ...

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices have used devices prepared by spin coating, a process that is not amenable to large-scale fabrication. This mismatch in device fabrication makes it difficult to translate quantitative results obtained in the laboratory to the commercial level, making optimization difficult. Using a mini-slot die coater, this mismatch can be resolved by translating the commercial process to the laboratory and characterizing the structure formation in the active layer of the device in real time and in situ as films are coated onto a substrate. The evolution of the morphology was characterized under different conditions, allowing us to propose a mechanism by which the structures form and grow. This mini-slot die coater offers a simple, convenient, material efficient route by which the morphology in the active layer can be optimized under industrially relevant conditions. The goal of this protocol is to show experimental details of how a solar cell device is fabricated using a mini-slot die coater and technical details of running in situ structure characterization using the mini-slot die coater.

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Here, we present a protocol to fabricate organic thin film solar cells using a mini-slot die coater and related in-line structure characterizations using synchrotron scattering techniques.

Polymer-based materials hold promise as low-cost, flexible efficient photovoltaic devices. Most laboratory efforts to achieve high performance devices ...

Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS)

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long and hollow glassy carbon microfibers derived from human hairs is introduced. The long and hollow carbon structures were made by the pyrolysis of human hair at 900 &#176;C in a N2 atmosphere. The morphology and chemical composition of natural and pyrolyzed human hairs were investigated using scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX), respectively, to estimate the physical and chemical changes due to pyrolysis. Raman spectroscopy was used to confirm the glassy nature of the carbon microstructures. Pyrolyzed hair carbon was introduced to modify screen-printed carbon electrodes ; the modified electrodes were then applied to the electrochemical sensing of dopamine and ascorbic acid. Sensing performance of the modified sensors was improved as compared to the unmodified sensors. To obtain the desired carbon structure design, carbon micro-/nanoelectromechanical system (C-MEMS/C-NEMS) technology was developed. The most common C-MEMS/C-NEMS fabrication process consists of two steps: (i) the patterning of a carbon-rich base material, such as a photosensitive polymer, using photolithography; and (ii) carbonization through the pyrolysis of the patterned polymer in an oxygen-free environment. The C-MEMS/NEMS process has been widely used to develop microelectronic devices for various applications, including in micro-batteries, supercapacitors, glucose sensors, gas sensors, fuel cells, and triboelectric nanogenerators. Here, recent developments of a high-aspect ratio solid and hollow carbon microstructures with SU8 photoresists are discussed. The structural shrinkage during pyrolysis was investigated using confocal microscopy and SEM. Raman spectroscopy was used to confirm the crystallinity of the structure, and the atomic percentage of the elements present in the material before and after pyrolysis was measured using EDX.

Fabrication of 3D Carbon Microelectromechanical Systems C-MEMS

Long and hollow glassy carbon microfibers were fabricated based on the pyrolysis of a natural product, human hair. The two fabrication steps of carbon microelectromechanical and carbon nanoelectromechanical systems, or C-MEMS and C-NEMS, are: (i) photolithography of a carbon-rich polymer precursor and (ii) pyrolysis of the patterned polymer precursor.

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long ...

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of gamma rays created when neutrons interact with soil elements. The main parts of the INS system are a pulsed neutron generator, NaI(Tl) gamma detectors, split electronics to separate gamma spectra due to INS and thermo-neutron capture (TNC) processes, and software for gamma spectra acquisition and data processing. This method has several advantages over other methods in that it is a non-destructive in situ method that measures the average carbon content in large soil volumes, is negligibly impacted by local sharp changes in soil carbon, and can be used in stationary or scanning modes. The result of the INS method is the carbon content from a site with a footprint of ~2.5 - 3 m2 in the stationary regime, or the average carbon content of the traversed area in the scanning regime. The measurement range of the current INS system is &#62;1.5 carbon weight % (standard deviation &#177; 0.3 w%) in the upper 10 cm soil layer for a 1 hmeasurement.

Here, we present the protocol for in situ measurement of soil carbon using the neutron-gamma technique for single point measurements (static mode) or field averages (scanning mode). We also describe system construction and elaborate data treatment procedures.

The herein described application of the inelastic neutron scattering (INS) method for soil carbon analysis is based on the registration and analysis of ...

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

Radio Frequency Magnetron Sputtering of GdBa2Cu3O7&#8722;&#948;/ La0.67Sr0.33MnO3 Quasi-bilayer Films on SrTiO3 (STO) Single-crystal Substrates

Here, we demonstrate a method of coating ferromagnetic La0.67Sr0.33MnO3 (LSMO) nanoparticles on (001) SrTiO3 (STO) single-crystal substrates by radio frequency (RF) magnetron sputtering. LSMO nanoparticles were deposited with diameters from 10 to 20 nm and heights between 20 and 50 nm. At the same time, (Gd) Ba2Cu3O7&#8722;&#948; ((Gd) BCO) films were fabricated on both undecorated and LSMO nanoparticle decorated STO substrates using RF magnetron sputtering. This report also describes the properties of GdBa2Cu3O7&#8722;&#948;/ La0.67Sr0.33MnO3 quasi-bilayer films structures (e.g., crystalline phase, morphology, chemical composition); magnetization, magneto-transport, and superconducting transport properties were also evaluated.

Radio Frequency Magnetron Sputtering of GdBa2Cu3O7ÃƒÆ’Ã‚Â¢Ãƒâ€¹Ã¢â‚¬Â 'ÃƒÆ’Ã…Â½ Â´/ La0.67Sr0.33MnO3 Quasi-bilayer Films on SrTiO3 STO Single-crystal Substrates

Here, we present a protocol to grow LSMO nanoparticles and (Gd) BCO films on (001) SrTiO3 (STO) single-crystal substrates by radio frequency (RF)-sputtering.

Here, we demonstrate a method of coating ferromagnetic La0.67Sr0.33MnO3 (LSMO) nanoparticles on (001) SrTiO3 (STO) single-crystal substrates by radio ...

Hybrid Printing for the Fabrication of Smart Sensors

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, three substrates (acrylate, ceramics, and copper) are prepared. To determine the resulting material properties of these substrates, profilometer, contact angle, scanning electron microscope (SEM), and focused ion beam (FIB) measurements are done. The achievable printing resolution and suitable drop volume for each substrate are, then, found through the drop size tests. Then, layers of insulating and conductive ink are inkjet printed alternately to fabricate the target sensor structures. After each printing step, the respective layers are individually treated by photonic curing. The parameters used for the curing of each layer are adapted depending on the printed ink, as well as on the surface properties of the respective substrate. To confirm the resulting conductivity and to determine the quality of the printed surface, four-point probe and profilometer measurements are done. Finally, a measurement set-up and results achieved by such an all-printed sensor system are shown to demonstrate the achievable quality.

Here we present a protocol for the fabrication of inkjet-printed multilayer sensor structures on additively manufactured substrates and foil.

A method to combine additively manufactured substrates or foils and multilayer inkjet printing for the fabrication of sensor devices is presented. First, ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

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Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

Fabrication of Silica Ultra High Quality Factor Microresonators

Preparation and Reactivity of Gasless Nanostructured Energetic Materials

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

Printing Fabrication of Bulk Heterojunction Solar Cells and In Situ Morphology Characterization

Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS)

Measurements of Soil Carbon by Neutron-Gamma Analysis in Static and Scanning Modes

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Radio Frequency Magnetron Sputtering of GdBa₂Cu₃O₇₋_δ/ La_0.67Sr_0.33MnO₃ Quasi-bilayer Films on SrTiO₃ (STO) Single-crystal Substrates

Hybrid Printing for the Fabrication of Smart Sensors