Name: bulk and thin film synthesis of compositionally variant entropy-stabilized oxides
Uploaded: 2018-05-29T15:00:00.000+00:00
Duration: 9 min 41 s
Description: Watch this Scientific Journal Video about Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides at JoVE.com

This work was funded in part by National Science Foundation grant No. DMR-0420785 (XPS). We thank the University of Michigan&#39;s Michigan Center for Materials Characterization, (MC)2, for its assistance with XPS, and the University of Michigan Van Vlack laboratory for XRD. We would also like to thank Thomas Kratofil for his assistance with bulk materials preparation.

Caution: Wear necessary personal protective equipment (PPE) including close-toed shoes, full length pants, safety glasses, particulate filtration mask, lab coat, and gloves as oxide powders pose a risk for skin contact irritation and eye contact irritation. Consult all relevant material safety data sheets before beginning for additional PPE requirements. Synthesis should be done with the use of engineering controls such as a fume hood.
1. Bulk Synthesis of Entropy-stabilized Oxides
<ol>
	<li>Mass Calculation of Constituent Oxide Powders
	<ol>
		<li>Estimate the total desired mass of the target by multiplying the desired volume by the average density of the constituent binary oxides. 
		<img alt="Equation 3" src="/files/ftp_upload/57746/57746eq3v2.jpg" /> 
		<img alt="Equation 4" src="/files/ftp_upload/57746/57746eq4.jpg" /> 
		where <img alt="Equation 5" src="/files/ftp_upload/57746/57746eq5.jpg" /> and <img alt="Equation 6" src="/files/ftp_upload/57746/57746eq6.jpg" /> are the mole fraction and the density of the <img alt="Equation 7" src="/files/ftp_upload/57746/57746eq7.jpg" />th component. For a 1&#34; (2.54 cm) diameter, &#8539;&#34; (0.3175 cm) thick sample, the target volume is <img alt="Equation 8" src="/files/ftp_upload/57746/57746eq8.jpg" />1.7 cm3.</li>
		<li>Determine the required moles of each component by dividing this target mass by the average molar mass of the constituent binary oxides. 
		<img alt="Equation 9" src="/files/ftp_upload/57746/57746eq9v2.jpg" /> 
		<img alt="Equation 10" src="/files/ftp_upload/57746/57746eq10.jpg" /> 
		where <img alt="Equation 11" src="/files/ftp_upload/57746/57746eq11.jpg" /> is the molar mass of the <img alt="Equation 7" src="/files/ftp_upload/57746/57746eq7.jpg" />th component. Convert the number of moles, <img alt="Equation 12" src="/files/ftp_upload/57746/57746eq12.jpg" />, back to grams by 
		<img alt="Equation 13" src="/files/ftp_upload/57746/57746eq13.jpg" /> 
		NOTE: The masses of constituents and targeted compositions of the materials synthesized here are given in Tables 1 and 2.</li>
	</ol>
	</li>
	<li>Preprocessing of Oxide Powders
	<ol>
		<li>Clean an agate pestle and mortar by etching with 20 mL of aqua regia (HNO3 + 3 HCl). Pour the acid into the mortar and grind with the pestle until the bottom is clear. Dispose of the acid properly and rinse with water.</li>
		<li>Combine 0.559 g of MgO, 1.103 g of CoO, 1.035 g of NiO, 1.103 g of CuO, and 1.129 g of ZnO (for equimolar composition) powders in the clean mortar.</li>
		<li>Using the clean pestle, grind the powder using clockwise motions for 20 turns, then 20 counterclockwise turns. Repeat this process for at least 45 min. Use a clean metal spatula to remove powder from the sides of the mortar and brush the powder down to the center of the mortar. 
		NOTE: Powder mixing and grinding are complete when the powder is homogenous and grey-black in color, appears finely ground, and feels smooth.</li>
		<li>Transfer the powder into a clean, sealable container for transport.</li>
	</ol>
	</li>
	<li>Ceramic Pellet Pressing 
	CAUTION: Wear gloves and safety glasses when assembling the die and while the press is in use. Perform entire die cleaning and assembly steps on a clean paper surface. The components used are shown in Figure 2.
	<ol>
		<li>Lubricate the sides and interior face of the small bottom plunger (labelled C in Figure 2a and 2b) of the die with mineral oil and insert into the die cylinder until it is flush with the bottom.</li>
		<li>Roll a weigh paper into the cavity of the die so that the sides of the die are covered. Pour the powder into the bottom of the die. Without allowing the small plunger to fall out of the die, gently tap the part on the counter to remove any air pockets and level the powder. Carefully remove the weigh paper.</li>
		<li>Add a small amount of acetone to the powder in the cavity of the die to form a slurry. This enables grain flow while the target is under pressure and inhibits the formation of voids.</li>
		<li>Lubricate the sides and interior face of the plunger (part B in Figure 2a and 2b) with paraffin oil, being careful to not disturb the powder. Insert this part into the die. Place the assembled die into the pressing machine as pictured in Figure 2c, including the top and bottom plates (parts D in Figure 2a and 2b) to provide an even surface.</li>
		<li>Place die in the cold uniaxial press. Pump the press arm until 200 MPa is reached. Allow the press to sit in the compressed state for 20 min. The pressure will relax with time as the powder densifies. Add pressure as needed to maintain 200 MPa for the duration of pressing. Wipe away any excess solvent that leaks out of the die.</li>
		<li>Release the press pressure. Carefully remove the top and bottom plates. Position the removal sheath and removal piston as shown in Figure 2c. Press slowly, removing the small die piece from the assembly before exposing the pressed target. Press the assembly carefully until the target is exposed from the die. Carefully remove the green body and transfer to a crucible for sintering.</li>
	</ol>
	</li>
	<li>Ceramic sintering 
	CAUTION: Target materials will be quenched from high temperatures. Wear heat resistant gloves and a face shield when removing the crucible from the hot furnace.
	<ol>
		<li>Obtain an alumina crucible that will fit the pressed powder and a 2 mm layer of Yttria-Stabilized Zirconia (YSZ) 0.1&#8211;0.2 mm beads. Coat the bottom of the crucible with YSZ beads. 
		NOTE: The coating should be approximately 2 mm in thickness to ensure that the target does not contact the bottom of the crucible.</li>
		<li>Slowly and carefully transfer the pressed target to the center of the crucible.</li>
		<li>Using metal tongs, carefully transport the crucible to the sintering furnace. Increase the temperature to 1100 &#176;C at 50 &#176;C min-1. Sinter the target for 24 h at 1,100 &#176;C in an air atmosphere.</li>
		<li>While at 1100 &#176;C, remove the crucible from the furnace. Using tongs, quickly quench the target in room temperature water. The target will sputter for ~30 s, then remove it from the water and set to dry.</li>
		<li>Once target is cool and dry, measure the target density and compare to the theoretical value, <img alt="Equation 14" src="/files/ftp_upload/57746/57746eq14v2.jpg" />, calculated in Part 1. Measure the mass of the target on the balance used previously, and measure the dimensions using calipers. The ratio of the measured density to the estimated value, <img alt="Equation 15" src="/files/ftp_upload/57746/57746eq15.jpg" />, gives the percent theoretical density. 
		NOTE: After the synthesis, the density is usually ~80% of the theoretical density.</li>
		<li>For higher density, regrind the sintered target using the pestle and mortar and repeat the Bulk Synthesis procedure from step 1.2.3. After the second sintering, determine the density of the target. 
		NOTE: Usually the measured density is <img alt="Equation 16" src="/files/ftp_upload/57746/57746eq16.jpg" /> theoretical density, which is suitable for pulsed laser deposition (PLD).</li>
	</ol>
	</li>
</ol>
2. PLD of ESO Single Crystal Films
<ol>
	<li>Target preparation
	<ol>
		<li>The bulk ceramic pellets synthesized in step 1 will now serve as deposition sources (targets). Polish the target(s) in a circular motion using progressive (320/600/800/1,200) grits of SiC paper until the surface is reflective and uniform.</li>
		<li>Place the targets on the rotating carousel inside the chamber and place a ~2 cm x 2 cm piece of burn paper on the final target in the beam path.</li>
		<li>Measure the laser spot size by firing a single shot at the target and measuring the resulting burn mark across both axes. If the spot size is not correct, adjust the focusing lens (Figure 3a). Adjust the measured spot size until an ellipse, 0.27 cm x 0.24 cm across both axes is achieved.</li>
		<li>Remove the burn paper and close the door for evacuation. Evacuate the chamber using a dry scroll roughing pump to a pressure of 6.7 Pa, at which point the turbo pump can be spun up to a rate of 1,000 Hz.</li>
		<li>Pump out the chamber to a base pressure of at least 1.3 x 10-5 Pa as measured by an ion gauge. Once reached, reduce the turbo to a speed of 200 Hz to allow the use of process gas during the growth.</li>
	</ol>
	</li>
	<li>Substrate Preparation
	<ol>
		<li>Clean a single crystalline, one side polished, 0.5 mm thick MgO substrate by sonication for 2 min each in semiconductor grade trichloroethylene (TCE), semiconductor grade acetone, and high purity isopropanol (IPA).</li>
		<li>Blow the substrate off with ultra-dry, compressed N2 gas, and attach the substrate to the substrate platen (Figure 3b) with a small amount of thermally conductive silver paint. Heat the substrate and platen to &#176;C for 10 min on a hot plate to cure the silver paint.</li>
		<li>Using the external transfer tool, place the substrate holder on the transfer arm in the chamber load lock, then seal and pump out the chamber to a pressure of at least 1.3 x 10-4 Pa.</li>
		<li>Transfer the substrate into the growth chamber by opening the gate valve between the two and using the transfer arm to place the substrate platen on the heater assembly.</li>
		<li>Retract the transfer arm back into the load lock and seal the gate. Lower the heater using the screw assembly on top of the chamber.</li>
	</ol>
	</li>
	<li>Laser Energy and Fluence 
	NOTE: Deposition is enabled by the irradiation from a 248 nm KrF pulsed excimer laser. The laser pulse width is ~20 ns.
	<ol>
		<li>Measure the laser energy using an energy meter placed in the beam path, just before entering the chamber (Figure 3a). Determine the mean energy after irradiating the photodiode with 50 pulses at a rate of 2 Hz.</li>
		<li>Vary the excitation voltage of the laser until an average pulse energy of 310 mJ is reached with &#177; 10 mJ stability. Remove the energy meter from the beam path to allow the laser to pass into the chamber. 
		NOTE: Using a laser attenuation of the chamber window of 10%, the configuration above gives a fluence of 2.55 J cm-2. The substrate-target distance in this work is 7 cm. A different substrate-target difference may change ideal deposition conditions and growth rate.</li>
	</ol>
	</li>
	<li>Deposition
	<ol>
		<li>Before growth, heat the substrate to 1,000 &#176;C for 30 min at a rate 30 &#176;C min-1 in vacuum to dehydroxylize the surface of MgO crystal. Reduce the temperature to 300 &#176;C at 30&#176; min-1 and allow to equilibrate for 10 min. 
		NOTE: Our reported temperatures are determined by a thermocouple within the heater block.</li>
		<li>Flow ultra-high purity (99.999%) O2 gas into the chamber to reach a pressure of 6.7 Pa. 
		NOTE: When oxygen flown into the chamber, the pressure is measured using a barotron gauge. The gas is introduced using a mass flow controller, as part of a closed loop system which stabilizes chamber pressure during growth.</li>
		<li>Clean the targets of any remaining contaminants and prepare them for growth by pre-ablation. Set the selected target to raster and rotate, so that the laser is not hitting the same spot each time, ensure that the substrate shutter is closed, and ablate the target for 2,000 pulses at a rate of 5 Hz. 
		NOTE: The target is now prepared, and the system is at the correct conditions (temperature, pressure, fluence) for deposition.</li>
		<li>Open the shutter before deposition. At these conditions, 10,000 pulses at 6 Hz produces an ~80 nm thick film. 
		NOTE: This growth rate was determined by X-ray reflectivity in previous work16.</li>
		<li>After deposition, increase the oxygen partial pressure to 133 Pa (1.0 torr) to inhibit the formation of oxygen vacancies. Reduce the sample temperature to 40 &#176;C at 10 &#176;min-1. Once 40 &#176;C is reached, close the flow of oxygen and, after the stabilization of pressure, open the gate valve between the growth chamber and the load lock. Raise the heater and use the transfer arm to remove the substrate platen from the assembly back into the load lock.</li>
		<li>Vent the load lock to atmosphere and remove the sample using the external transfer tool. Remove the sample from the platen using a razor blade and polish the platen to take off the remaining silver paint and deposited material. Repeat the procedure starting from step 2.2 for additional film growth.</li>
	</ol>
	</li>
</ol>

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D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Relaxor+ferroelectricity+in+strained+epitaxial+SrTiO3+thin+films+on+DyScO3+substrates.">Relaxor ferroelectricity in strained epitaxial SrTiO3 thin films on DyScO3 substrates.</a> Appl Phys Lett. 88 (19), 192907 (2006).</li><li>Schlom, D. G., Chen, L. Q., Pan, X., Schmehl, A., Zurbuchen, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Thin+Film+Approach+to+Engineering+Functionality+into+Oxides.">A Thin Film Approach to Engineering Functionality into Oxides.</a> J Am Ceram Soc. 91 (8), 2429-2454 (2008).</li><li>Damodaran, A. R., Breckenfeld, E., Chen, Z., Lee, S., Martin, L. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enhancement+of+Ferroelectric+Curie+Temperature+in+BaTiO3+Films+via+Strain-Induced+Defect+Dipole+Alignment.">Enhancement of Ferroelectric Curie Temperature in BaTiO3 Films via Strain-Induced Defect Dipole Alignment.</a> Adv Mater. 26 (36), 6341-6347 (2014).</li></ol>

We have nothing to disclose.

We have described and shown a protocol for the synthesis of bulk and high-quality, single crystalline films of (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) entropy-stabilized oxides. We expect these synthesis techniques to be applicable to a wide range of entropy-stabilized oxide compositions as more are discovere...

Since the discovery of high-entropy metal alloys in 2004, high-entropy materials have attracted significant interest due to the properties such as increased hardness1,2,3, toughness4,5, and corrosion resistance3,6. Recently, high-entropy oxides7,8 and borides9 have been discovered, opening up a large playground for material enthusiasts. Oxides, in particular, can demonstrate useful and dynamic functional properties such as ferroelectricity10, magnetoelectricity11,12, thermoelectricity13, and superconductivity14. Entropy-stabilized oxides (ESOs) have recently been shown to possess interesting, compositionally-dependent functional properties15,16, despite the significant disorder, making this new class of materials particularly exciting.
Entropy-stabilized materials are chemically homogeneous, multicomponent (typically having five or more constituents), single-phase materials where the configurational entropic contribution (<img alt="Equation 1" src="/files/ftp_upload/57746/57746eq1.jpg" />) to the Gibbs free energy (<img alt="Equation 2" src="/files/ftp_upload/57746/57746eq2.jpg" />) is significant enough to drive the formation of a single phase solid solution17. The synthesis of multicomponent ESOs, where cationic configurational disorder is observed across the cation sites, requires precise control over the composition, temperature, deposition rate, quench rate, and quench temperature7,16. This method seeks to enable the practitioner the ability to synthesize phase pure and chemically homogeneous entropy-stabilized oxide ceramic pellets and phase pure, single crystalline, flat thin films of the desired stoichiometry. Bulk materials can be synthesized with greater than 90% theoretical density enabling the study of the electronic, magnetic, and structural properties or use as sources for thin film physical vapor deposition (PVD) techniques. As the entropy-stabilized oxides considered here have five cations, thin film PVD techniques that employ five sources, such as molecular beam epitaxy (MBE) or co-sputtering, will be presented with the challenge of depositing chemically homogenous thin films due to flux drift. This protocol results in chemically homogenous, single crystalline, flat (root-mean-square (RMS) roughness of ~0.15 nm) entropy-stabilized oxide thin films from a single material source, which are shown to possess the nominal chemical composition. This thin film synthesis protocol may be enhanced by the inclusion of in situ electron or optical characterization techniques for real-time monitoring of the synthesis and refined quality control. Expected limitations of this method stem from laser energy drift which may limit the thickness of high quality films to be below 1 &#956;m.
Despite the significant advances in the growth and characterization of thin film oxide materials10,18,19,20,21, the correlation between stereochemistry and electronic structure in oxides can lead to significant differences in the final material stemming from seemingly insignificant methodological differences. Furthermore, the field of multicomponent entropy-stabilized oxides is rather nascent, with only two current reports of thin film synthesis in the literature7,16. ESOs lend themselves particularly well to this process, circumventing challenges that would be presented by chemical vapor deposition and molecular beam epitaxy. Here, we provide a detailed synthesis protocol of bulk and thin films ESOs (Figure 1), in order to minimize materials processing difficulties, unintended property variations, and improve the acceleration of discovery in the field.

<table><tbody><tr><td>MAGNESIUM OXIDE 99.95%</td><td>Fisher</td><td>AA1468422</td><td></td></tr><tr><td>COBALT(II) OXIDE, 99.995%</td><td>Fisher</td><td>AA4435414</td><td></td></tr><tr><td>NICKEL(II) OXIDE 99.998%</td><td>Fisher</td><td>AA1081914</td><td></td></tr><tr><td>COPPER(II) OXIDE 99.995%</td><td>Fisher</td><td>AA1070014</td><td></td></tr><tr><td>ZINC OXIDE 99.99%</td><td>Fisher</td><td>AA8781230</td><td></td></tr><tr><td>TRICHLROETHLENE SEMICNDTR 9</td><td>Fisher</td><td>AA39744K7</td><td></td></tr><tr><td>ACETONE SEMICNDTR GRD 99.5%</td><td>Fisher</td><td>AA19392K7</td><td></td></tr><tr><td>2-PROPANOL ACS 99.5%</td><td>Fisher</td><td>A416S4</td><td></td></tr><tr><td>Mineral oil, pure</td><td>Acros Organics</td><td>AC415080010</td><td></td></tr><tr><td>alumina crucible</td><td>MTI Corporation</td><td>eq-ca-l50w40h20</td><td></td></tr><tr><td>ZIRCONIA (YSZ) GRINDING MEDIA</td><td>Inframat Advanced Materials</td><td>4039GM-S010</td><td></td></tr><tr><td>SiC paper 320/600/800/1200</td><td>South Bay Technology</td><td>SDA08032-25</td><td></td></tr><tr><td>MgO (100) substrate, 5x5x0.5 mm, 1SP</td><td>MTI Corporation</td><td>MGa050505S1</td><td></td></tr><tr><td>OXYGEN COMPRESSED ULTRA HIGH PURITY GRADE, 99.999%</td><td>Cryogenic Gases</td><td>OXYUHP</td><td></td></tr><tr><td>NITROGEN COMPRESSED EXTRA DRY GRADE</td><td>Cryogenic Gases</td><td>NITEX</td><td></td></tr></tbody></table>

bulk and thin film synthesis of compositionally variant entropy-stabilized oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

X-ray diffraction (XRD) spectra were taken of both the prepared (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) bulk ceramics (Figure 4a) and deposited thin films (Figure 4b). These data show that the samples are single phase...

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Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

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9.4K Views.  University of Michigan. The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

Video: Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Fabrication of Spatially Confined Complex Oxides

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices 1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from ...

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

Chemistry

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, ...

Synthesizing Sodium Tungstate and Sodium Molybdate Microcapsules via Bacterial Mineral Excretion

We present a method, the bacterial mineral excretion (BME), for synthesizing two kinds of microcapsules, sodium tungstate and sodium molybdate, and the two metal oxides&#39; corresponding nanoparticles&#8212;the former being as small as 22 nm and the latter 15 nm. We fed two strains of bacteria, Shewanella algae and Pandoraea sp., with various concentrations of tungstate or molybdate ions. The concentrations of tungstate and molybdate were adjusted to make microcapsules of different length-to-diameter ratios. We found that the higher the concentration the smaller the nanoparticles were. The nanoparticles came in with three length-to-diameter ratios: 10:1, 3:1 and 1:1, which were achieved by feeding the bacteria respectively with a low concentration, a medium concentration, and a high concentration. The images of the hollow microcapsules were taken via the scanning electron microsphere (SEM). Their crystal structures were verified by X-ray diffraction (XRD)&#8212;the crystal structure of molybdate microcapsules is Na2MoO4 and that of tungstate microcapsules is Na2WO4 with Na2W2O7. These syntheses all were accomplished under a near ambient condition.

This work presents a protocol for manufacture sodium tungstate and sodium molybdate microcapsules via bacteria and their corresponding nanoparticles.

We present a method, the bacterial mineral excretion (BME), for synthesizing two kinds of microcapsules, sodium tungstate and sodium molybdate, and the ...

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Chemical Synthesis of Porous Barium Titanate Thin Film and Thermal Stabilization of Ferroelectric Phase by Porosity-Induced Strain

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its well-balanced ferroelectricity, piezoelectricity, and dielectric constant. In addition, BT does not contain any toxic elements. Therefore, it is considered to be an eco-friendly material, which has attracted considerable interest as a replacement for lead zirconate titanate (PZT). However, bulk BT loses its ferroelectricity at approximately 130 &#176;C, thus, it cannot be used at high temperatures. Because of the growing demand for high-temperature ferroelectric materials, it is important to enhance the thermal stability of ferroelectricity in BT. In previous studies, strain originating from the lattice mismatch at hetero-interfaces has been used. However, the sample preparation in this approach requires complicated and expensive physical processes, which are undesirable for practical applications.
In this study, we propose a chemical synthesis of a porous material as an alternative means of introducing strain. We synthesized a porous BT thin film using a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles were used as an organic template. Through a series of studies, we clarified that the introduction of pores had a similar effect on distorting the BT crystal lattice, to that of a hetero-interface, leading to the enhancement and stabilization of ferroelectricity. Owing to its simplicity and cost effectiveness, this fabrication process has considerable advantages over conventional methods.

Here, we present a protocol for the synthesis of porous barium titanate (BaTiO3) thin film by a surfactant-assisted sol-gel method, in which self-assembled amphipathic surfactant micelles are used as an organic template.

Barium titanate (BaTiO3, hereafter BT) is an established ferroelectric material first discovered in the 1940s and still widely used because of its ...

Molten-Salt Synthesis of Complex Metal Oxide Nanoparticles

The development of feasible synthesis methods is critical for the successful exploration of novel properties and potential applications of nanomaterials. Here, we introduce the molten-salt synthesis (MSS) method for making metal oxide nanomaterials. Advantages over other methods include its simplicity, greenness, reliability, scalability, and generalizability. Using pyrochlore lanthanum hafnium oxide (La2Hf2O7) as a representative, we describe the MSS protocol for the successful synthesis of complex metal oxide nanoparticles (NPs). Furthermore, this method has the unique ability to produce NPs with different material features by changing various synthesis parameters such as pH, temperature, duration, and post-annealing. By fine-tuning these parameters, we are able to synthesize highly uniform, non-agglomerated, and highly crystalline NPs. As a specific example, we vary the particle size of the La2Hf2O7&#160;NPs by changing the concentration of the ammonium hydroxide solution used in the MSS process, which allows us to further explore the effect of particle size on various properties. It is expected that the MSS method will become a more popular synthesis method for nanomaterials and more widely employed in the nanoscience and nanotechnology community in the upcoming years.

Here, we demonstrate a unique, relatively low-temperature, molten-salt synthesis method for preparing uniform complex metal oxide lanthanum hafnate nanoparticles.

The development of feasible synthesis methods is critical for the successful exploration of novel properties and potential applications of nanomaterials. ...

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 ...

Stable Aqueous Suspensions of Manganese Ferrite Clusters with Tunable Nanoscale Dimension and Composition

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse applications. Here we describe how to form these materials in a hydrothermal process that permits the independent control of product cluster size (from 30 to 120 nm) and manganese content of the resulting material. Parameters such as the total amount of water added to the alcoholic reaction media and the ratio of manganese to iron precursor are important factors in achieving multiple types of MFC nanoscale products. A fast purification method uses magnetic separation to recover the materials making production of grams of magnetic nanomaterials quite efficient. We overcome the challenge of magnetic nanomaterial aggregation by applying highly charged sulfonate polymers to the surface of these nanomaterials yielding colloidally stable MFCs that remain non-aggregating even in highly saline environments. These non-aggregating, uniform, and tunable materials are excellent prospective materials for biomedical and environmental applications.

We report a one-pot hydrothermal synthesis of manganese ferrite clusters (MFCs) that offers independent control over material dimension and composition. Magnetic separation allows rapid purification while surface functionalization using sulfonated polymers ensures the materials are non-aggregating in biologically relevant medium. The resulting products are well positioned for biomedical applications.

Manganese ferrite clusters (MFCs) are spherical assemblies of tens to hundreds of primary nanocrystals whose magnetic properties are valuable in diverse ...

Metal Oxide Heterojunction for Photocatalytic Activities

There is a significant global demand for improvements in synthesis techniques and their optimal characteristics, especially for industrial-scale applications. Sol-gel-based solution combustion synthesis (SG-SCS) is a simple method to produce ordered porous materials. In this regard, Pearson&#39;s hard and soft acids and bases theory assists in selecting host-dopant reactivity to form a proper heterojunction.
The formation of a heterojunction also changes the essential properties of the materials, improving photocatalysis via charge transfer or synergistic activities. A calcination temperature of 500 &#176;C is ideal for this process based on the results of the stability assessment via a differential thermogravimetry ratio analysis (DTG).
The nanoscale dimensions of the nanoparticles (NPs) and nanocomposites (NCs) generated were validated using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM). Furthermore, the scanning electron microscopy micrographs and BET analyses confirmed the porosity nature of the materials. HRTEM, X-ray photoelectron spectroscopy, and energy-dispersive X-ray investigations established the materials composition. The study found that NCs degraded the acid orange 8 (AO8) color more efficiently than bare ZnO.

The development of a heterojunction boosts the photocatalytic activities of solution combustion synthesis, which is a time-/energy-efficient process. Advanced analytical characterization techniques were used in this protocol to evaluate the materials&#39; characteristics, and nanocomposites demonstrated improved acid orange-8 dye degradation.

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

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