Name: niobium oxide films deposited by reactive sputtering: effect of oxygen flow rate
Uploaded: 2019-09-28T14:30:00
Description: Watch this Scientific Journal Video about Niobium Oxide Films Deposited by Reactive Sputtering: Effect of Oxygen Flow Rate at JoVE.com

The work was supported by Funda&#231;&#227;o de Amparo &#224; Pesquisa do Estado de S&#227;o Paulo (FAPESP), Centro de&#160;Desenvolvimento de Materiais Cer&#226;micos (CDMF- FAPESP&#160;N&#186; 2013/07296-2, 2017/11072-3, 2013/09963-6 and 2017/18916-2). Special thanks to Professor M&#225;ximo Siu Li for PL measurements.

1. Etching and cleaning the substrate
<ol>
	<li>Using a glass cutting system, form 2.5 x 2.5 cm substrates of fluoride thin oxide (FTO).</li>
	<li>Protect part of the substrate surface with a thermal tape leaving 0.5 cm of one side exposed.</li>
	<li>Deposit a small amount of zinc powder (enough to cover the area to be etched) on the top of the exposed FTO and drop concentrated hydrochloric acid (HCl) on the zinc powder slowly until all zinc powder is consumed by the reaction. Immediately after, rinse the substrate wit...

<ol>
	<li>Wasa, K., Kitabatake, M., Adachi, H. <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 materials technology : sputtering of compound materials. , (2004).</li><li>Kelly, P. J., Arnell, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Magnetron+sputtering:+A+review+of+recent+developments+and+applications.">Magnetron sputtering: A review of recent developments and applications.</a> Vacuum. 56, 159-172 (2000).</li><li>Chen, W. -. C., Peng, C. Y., Chang, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Heteroepitaxial+growth+of+TiN+film+on+MgO+(100)+by+reactive+magnetron+sputtering.">Heteroepitaxial growth of TiN film on MgO (100) by reactive magnetron sputtering.</a> Nanoscale Research Letters. 9, 551 (2014).</li><li>Guo, Q. X., 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=Heteroepitaxial+growth+of+gallium+nitride+on+(+1+1+1+)+GaAs+substrates+by+radio+frequency+magnetron+sputtering.">Heteroepitaxial growth of gallium nitride on ( 1 1 1 ) GaAs substrates by radio frequency magnetron sputtering.</a> Journal of Crystal Growth. 239, 1079-1083 (2002).</li><li>Berg, S., Nyberg, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fundamental+understanding+and+modeling+of+reactive+sputtering+processes.">Fundamental understanding and modeling of reactive sputtering processes.</a> Thin Solid films. (476), 215-230 (2005).</li><li>Wong, M. S., Sproul, W. D., Chu, X., Barnett, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reactive+magnetron+sputter+deposition+of+niobium+nitride+films.">Reactive magnetron sputter deposition of niobium nitride films.</a> Journal Vacuum Science &amp; Technology A: Vacuum, Surfaces and Films. 11, 1528-1533 (2002).</li><li>Zoita, C. N., Braic, L., Kiss, A., Braic, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+NbC+coatings+deposited+by+magnetron+sputtering+method.">Characterization of NbC coatings deposited by magnetron sputtering method.</a> Surface and Coatings Technology. 204, 2002-2005 (2010).</li><li>Nico, C., Monteiro, T., Gra&#231;a, M. P. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Niobium+oxides+and+niobates+physical+properties:+Review+and+prospects.">Niobium oxides and niobates physical properties: Review and prospects.</a> Progress in Materials Science. 80, 1-37 (2016).</li><li>Aegerter, M. A., Schmitt, M., Guo, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sol-gel+niobium+pentoxide+coatings:+Applications+to+photovoltaic+energy+conversion+and+electrochromism.">Sol-gel niobium pentoxide coatings: Applications to photovoltaic energy conversion and electrochromism.</a> International Journal of Photoenergy. 4, 1-10 (2002).</li><li>Fernandes, S. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hysteresis+dependence+on+CH3NH3PbI3+deposition+method+in+perovskite+solar+cells.">Hysteresis dependence on CH3NH3PbI3 deposition method in perovskite solar cells.</a> Proceedings of SPIE - International Society for Optics and Photonics. 9936, 9936 (2016).</li><li>Fernandes, S. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nb2O5hole+blocking+layer+for+hysteresis-free+perovskite+solar+cells.">Nb2O5hole blocking layer for hysteresis-free perovskite solar cells.</a> Materials Letters. 181, 103-107 (2016).</li><li>Hamada, K., Murakami, N., Tsubota, T., Ohno, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Solution-processed+amorphous+niobium+oxide+as+a+novel+electron+collection+layer+for+inverted+polymer+solar+cells.">Solution-processed amorphous niobium oxide as a novel electron collection layer for inverted polymer solar cells.</a> Chemical Physics Letters. 586, 81-84 (2013).</li><li>Aegerter, 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=Sol-gel+niobium+pentoxide:+A+promising+material+for+electrochromic+coatings,+batteries,+nanocrystalline+solar+cells+and+catalysis.">Sol-gel niobium pentoxide: A promising material for electrochromic coatings, batteries, nanocrystalline solar cells and catalysis.</a> Solar Energy Materials and Solar Cells. 68, 401-422 (2001).</li><li>Rani, R. A., Zoolfakar, A. S., O'Mullane, A. P., Austin, M. W., Kalantar-Zadeh, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thin+films+and+nanostructures+of+niobium+pentoxide:+fundamental+properties,+synthesis+methods+and+applications.">Thin films and nanostructures of niobium pentoxide: fundamental properties, synthesis methods and applications.</a> Journal Materials Chemistry A. 2, 15683-15703 (2014).</li><li>Foroughi-Abari, A., Cadien, K. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth,+structure+and+properties+of+sputtered+niobium+oxide+thin+films.">Growth, structure and properties of sputtered niobium oxide thin films.</a> Thin Solid Films. 519, 3068-3073 (2011).</li><li>Numata, Y., 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=Nb-doped+amorphous+titanium+oxide+compact+layer+for+formamidinium-based+high+efficiency+perovskite+solar+cells+by+low-temperature+fabrication.">Nb-doped amorphous titanium oxide compact layer for formamidinium-based high efficiency perovskite solar cells by low-temperature fabrication.</a> Journal Materials Chemistry A. 6, 9583-9591 (2018).</li><li>Gra&#231;a, M. P. F., Meireles, A., Nico, C., Valente, 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=Nb2O5+nanosize+powders+prepared+by+sol-gel+-+Structure,+morphology+and+dielectric+properties.">Nb2O5 nanosize powders prepared by sol-gel - Structure, morphology and dielectric properties.</a> Journal of Alloys and Compounds. 553, 177-182 (2013).</li><li>Kogo, A., Numata, Y., Ikegami, M., Miyasaka, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nb+2+O+5+Blocking+Layer+for+High+Open-circuit+Voltage+Perovskite+Solar+Cells.">Nb 2 O 5 Blocking Layer for High Open-circuit Voltage Perovskite Solar Cells.</a> Chemistry Letters. 44, 829-830 (2015).</li><li>Ueno, S., Fujihara, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+an+Nb2O5+nanolayer+coating+on+ZnO+electrodes+in+dye-sensitized+solar+cells.">Effect of an Nb2O5 nanolayer coating on ZnO electrodes in dye-sensitized solar cells.</a> Electrochimica Acta. 56, 2906-2913 (2011).</li><li>Fernandes, S. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploring+the+Properties+of+Niobium+Oxide+Films+for+Electron+Transport+Layers+in+Perovskite+Solar+Cells.">Exploring the Properties of Niobium Oxide Films for Electron Transport Layers in Perovskite Solar Cells.</a> Frontiers in Chemistry. 7, 1-9 (2019).</li><li>Shirani, A., 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=Tribologically+enhanced+self-healing+of+niobium+oxide+surfaces.">Tribologically enhanced self-healing of niobium oxide surfaces.</a> Surface and Coatings Technology. 364, 273-278 (2014).</li><li>Yan, J., 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=Nb2O5/TiO2+heterojunctions:+Synthesis+strategy+and+photocatalytic+activity.">Nb2O5/TiO2 heterojunctions: Synthesis strategy and photocatalytic activity.</a> Applied Catalysis B: Environmental. 152 (1), 280-288 (2014).</li></ol>

The niobium oxide films prepared in this work was used as electron transport layer in perovskite solar cells. The most important characteristic required for an electron transport layer is to prevent recombination, blocking holes and transferring efficiently electrons.
In this respect the use of reactive sputtering technique is advantageous since it produces dense and compact films. Also, as already mentioned, compared to sol-gel, anodization, hydrothermal, and chemical vapor deposition synthes...

The sputtering technique is widely used to deposit high-quality films. Its main application is in the semiconductor industry, although it is also used in surface coating for improvement in mechanical properties, and reflective layers1. The main advantage of sputtering is the possibility to deposit different materials over different substrates; the good reproducibility and control over the deposition parameters. The sputtering technique allows deposition of homogeneous films, with good adhesion over large areas and at low-cost when compared with other deposition methods like chemical vapor deposition (CVD), molecular beam epitaxy (MBE) and atomic layer deposition (ALD)1,2. Commonly, semiconductor films deposited by sputtering are amorphous or polycrystalline, however, there are some reports on epitaxial growth by sputtering3,4. Nevertheless, the sputtering process is highly complex and the range of the parameter is wide5, so in order to achieve high-quality films, a good comprehension of the process and parameter optimization is necessary for each material.
There are several articles reporting on the deposition of niobium oxide films by sputtering, as well as niobium nitride6 and niobium carbide7. Among Nb-oxides, niobium pentoxide (Nb2O5) is a transparent, air-stable and water-insoluble material that exhibits extensive polymorphism. It is an n-type semiconductor with band gap values ranging from 3.1 to 5.3 eV, giving these oxides a wide range of applications8,9,10,11,12,13,14,15,16,17,18,19. Nb2O5 has attracted considerable attention as a promising material to be used in perovskite solar cells due to its comparable electron injection efficiency and better chemical stability compared to titanium dioxide (TiO2). In addition, the band gap of Nb2O5 could improve the open-circuit voltage (Voc) of the cells14.
In this work, Nb2O5 was deposited by reactive sputtering under different oxygen flow rates. At low oxygen flow rates, the conductivity of the films were increased without making use of doping, which introduces impurities on the system. These films were used as electron transport layer in perovskite solar cells improving the performance of these cells. It was found that decreasing the amount of oxygen induces the formation of oxygen vacancies, which increases the conductivity of the films leading to solar cells with better efficiency.

<table>
	<tbody>
		<tr>
			<td>2-propanol</td>
			<td>Merck</td>
			<td>67-63-0</td>
			<td>solvent with maximum of 0.005% H2O</td>
		</tr>
		<tr>
			<td>4-tert-butylpyridine</td>
			<td>Sigma Aldrich</td>
			<td>3978-81-2</td>
			<td>chemical with 96% purity</td>
		</tr>
		<tr>
			<td>acetonitrile</td>
			<td>Sigma Aldrich</td>
			<td>75-05-8</td>
			<td>anhydrous solvent , 99.8% purity</td>
		</tr>
		<tr>
			<td>bis(trifluoromethane)sulfonimide lithium salt</td>
			<td>Sigma Aldrich</td>
			<td>90076-65-6</td>
			<td>chemical with &#8805;99.95% purity</td>
		</tr>
		<tr>
			<td>chlorobenzene</td>
			<td>Sigma Aldrich</td>
			<td>108-90-7</td>
			<td>anhydrous solvent , 99.8% purity</td>
		</tr>
		<tr>
			<td>ethanol</td>
			<td>Sigma Aldrich</td>
			<td>200-578-6</td>
			<td>solvent</td>
		</tr>
		<tr>
			<td>Fluorine doped tin oxide (SnO2:F) glass substrate</td>
			<td>Solaronix</td>
			<td>TCO22-7/LI</td>
			<td>substrate to deposit films</td>
		</tr>
		<tr>
			<td>Kaptom tape</td>
			<td>Usinainfo</td>
			<td>04227</td>
			<td>thermal tape used to cover the substrates</td>
		</tr>
		<tr>
			<td>Kurt J Lesker magnetron sputtering system</td>
			<td>Kurt J Lesker</td>
			<td>------</td>
			<td>Sputtering equipment used to deposit compact films</td>
		</tr>
		<tr>
			<td>Lead (II) iodide</td>
			<td>Alfa Aesar</td>
			<td>10101-63-0</td>
			<td>PbI2 salt- 99.998% purity</td>
		</tr>
		<tr>
			<td>methylammonium iodide</td>
			<td>Dyesol</td>
			<td>14965-49-2</td>
			<td>CH3NH3I salt</td>
		</tr>
		<tr>
			<td>N2,N2,N2&#8242;,N2&#8242;,N7,N7,N7&#8242;,N7&#8242;-octakis (4-methoxyphenyl)-9,9&#8242;-spirobi [9H-fluorene]-2,2&#8242;,7,7&#8242;-tetramine</td>
			<td>Sigma Aldrich</td>
			<td>207739-72-8</td>
			<td>Spiro-OMeTAD salt, 99% purity</td>
		</tr>
		<tr>
			<td>Niobium target of 3&#8221;</td>
			<td>CBMM- Brazilian Metallurgy and Mining Company</td>
			<td>------</td>
			<td>niobium sputtering target used in the sputtering system</td>
		</tr>
		<tr>
			<td>N-N dimethylformamide</td>
			<td>Merck</td>
			<td>68-12-2</td>
			<td>solvent with maximum of 0.003% H2O</td>
		</tr>
		<tr>
			<td>TiO2 paste</td>
			<td>Dyesol</td>
			<td>DSL 30NR-D</td>
			<td>titanium dioxide paste</td>
		</tr>
		<tr>
			<td>tris(2-(1H-pyrazol-1-yl)-4-tert-butylpyridine)cobalt(III) tri[bis(trifluoromethane)sulfonimide]</td>
			<td>Dyesol</td>
			<td>329768935</td>
			<td>FK 209 Co(III) TFSL salt</td>
		</tr>
	</tbody>
</table>

niobium oxide films deposited by reactive sputtering: effect of oxygen flow rate

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition parameters such as gas flow rate that results in changes on composition and thus in the film required properties. In this report, reactive sputtering is used to deposit niobium oxide films. A niobium target is used as metal source and different oxygen flow rates to deposit niobium oxide films. The oxygen flow rate was changed from 3 to 10 sccm. The films deposited under low oxygen flow rates show higher electrical conductivity and provide better perovskite solar cells when used as electron transport layer.

In the sputtering system, the deposition rate is strongly influenced by the oxygen flow rate. The deposition rate decreases when the oxygen flow is increased. Considering the present conditions of the target area used and plasma power, it is observed that from 3 to 4 sccm there is an expressive decrease on the deposition rate, however, when the oxygen is increased from 4 to 10 sccm it becomes less pronounced. In the regime of 3 sccm the deposition rate is 1.1 nm/s, decreasing abruptly to 0.1 nm/s for 10 sccm as seen in <...

Watch this Scientific Journal Video about Niobium Oxide Films Deposited by Reactive Sputtering: Effect of Oxygen Flow Rate at JoVE.com

Niobium Oxide Films Deposited by Reactive Sputtering: Effect of Oxygen Flow Rate

Here, we present a protocol for niobium oxide films deposition by reactive sputtering with different oxygen flow rates for use as an electron transport layer in perovskite solar cells.

Reactive sputtering is a versatile technique used to form compact films with excellent homogeneity. In addition, it allows easy control over deposition ...

In the reactive sputter technique it's possible to have a fine control of the parameters which allows to deposit niobium oxide fume with different stochiometer and preference. The main advantage of this technique is the deposition of homogenous fumes with good adhesion over large areas and at low cost and low hinders of production. It's important to pay attention to each step and to not skip any.Realizing how to handle equipment and the final appearance of the fumes helps to achieve a good deposition. Begin by protecting the substrate surface with a thermal tape, leaving 0.5 cm of one side exposed. Deposit enough zinc powder to cover the area to be etched on the top of the exposed fluoride thin oxide.Then slowly drop concentrated hydrochloric acid until all of the zinc powder is consumed by the reaction. Immediately wash the substrate with the ionized water. Remove the tape.And sonicate the substrate with soap for 15 minutes, followed by two times in water, acetone, and isopropanol alcohol. After fixing the substrate through a metal shadow mask, place the substrate into the sputtering chamber. After sealing the chamber, start the mechanic pump, and turn on the turbo molecular pump.When the vacuum reaches five times 10 to the negative five torr, open the water cooler system and turn on the substrate heating system. Set the temperature to 500 degrees Celsius, increasing 100 degrees Celsius every five minutes until it reaches the desired value. Set the argon to 40 SCCM, and the oxygen to three standard cubic centimeters per minute.Introduce argon into the chamber. And set the pressure to five times 10 to the negative three torr, and the radio frequency to 120 watts. Turn on the radio frequency.Using the impedance matching box to tune the frequency as necessary. If the plasma does not start, increase the pressure slowly until it reaches two times 10 to the negative two torr. Using a gate valve that can be opened or closed to change the pumping rate to set the pressure.Keep the plasma at 120 watts for 10 minutes to clean the Niobium target and to remove any oxide layer present in its surface. After stabilization, introduce Oxygen in to the chamber, set the RF power to 240 watts, and open the substrate shutter. Start the deposition and set the deposition time, to achieve a final thickness of 100 nanometers.As soon as the deposition is complete, close the shutter, turn off the radio frequency, close the gases, and decrease the substrate temperature. As the substrate temperature reaches room temperature, introduce air to re-establish the ambient pressure before opening the chamber, and removing the substrate. For solar cell construction, protect both sides of the substrate with a piece of tape and use a spin coater at 4, 000 rotations per minute for 30 seconds to deposit a mesoporous titanium dioxide layer onto the niobium oxide layer.Then place the substrate in the oven according to the indicated warming sequence. When the oven reaches room temperature, use the spin coater to deposit two layers of the lead iodide into the titanium dioxide layer at 6, 000 rotations per minute for 90 seconds. Placing the substrate onto a hot plate or 70 degrees Celsius for 10 minutes after each deposition.After the heat treatment, drop 300 milliliters of methylammonium iodide solution onto the lead iodide layers and wait 20 seconds before spinning at 4, 000 rotations per minute for 30 seconds. At the end of the spin, place the substrate on a hot plate for 10 minutes at 100 degrees Celsius, before depositing Spiro OMetTAD solution on top of the perovskite layer in the spin coater at 4, 000 rotations per minute for 30 seconds. Then store the films in desiccator in air overnight to oxidize Spiro OMetTAD.The next morning, scratch the perovskite film to expose the FTO. Use a shadow mask to deposit gold contact in an evaporator machine at a rate of 0.2 angstroms per second until the thickness reaches five nanometers, before increasing the rate to one angstrom per second to obtain 17 nanometers of gold contact. Then the cell is ready to be tested.In the sputtering system, the deposition rate is strongly influenced by the oxygen flow rate, decreasing when the oxygen flow increases. For example, from three to four SCCM, there is an expressive decrease on the deposition rate. When the oxygen is increased, from four to 10 SCCM however the deposition rate becomes less pronounced.The niobium oxide phase formed is dependent on the oxygen flow rate, and for flows less than three SCCM niobium dioxide is the main phase formed. For flows equal or higher than 3.5 SCCM, the oxygen volume is too high to generate niobium dioxide. Instead niobium pentoxide is observed as the main phase.Electronmicroscopy images show the nano metric spherical particles of the films deposited at three point five, four, and 10 SCCM. In contrast the film deposited at three SCCM reveals sheet shaped particles. The films deposited by reactive sputtering in different oxygen flow rates demonstrate different electrical properties.The conductivity of the films increases when three SCCM of oxygen is used. When the Oxygen flow rate is increased to three point five, four or 10 SCCM, a decrease in the conductivity is observed. The performance of perovskite solar cells also depends on the niobium oxide used.As a cell made with electron transport layers deposited at three point five SCCM has the best performance with the highest short circuit current. Remember to check that all of parameters are correctly set before starting the deposition of niobium oxide films. The Niobium oxides films can also be the cause that putting off chemical solutions.However, the metal does not allow the deposition of different stoichiometry. Is the development of parts that analyzes of how the conductivity of Niobium oxide fumes influences the performance of the perovskite solar cells. Take care when using the chemicals for the perovskite deposition and be sure to follow all of the laboratory safety rules.

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Research

JoVE Journal

Chemistry

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 ...

Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials

Supercritical fluid extraction and drying methods are well established in numerous applications for the synthesis and processing of porous materials. Herein, nitrogen is presented as a novel supercritical drying fluid for specialized applications such as in the processing of reactive porous materials, where carbon dioxide and other fluids are not appropriate due to their higher chemical reactivity. Nitrogen exhibits similar physical properties in the near-critical region of its phase diagram as compared to carbon dioxide: a widely tunable density up to ~1 g ml-1, modest critical pressure (3.4 MPa), and small molecular diameter of ~3.6 &#197;. The key to achieving a high solvation power of nitrogen is to apply a processing temperature in the range of 80-150 K, where the density of nitrogen is an order of magnitude higher than at similar pressures near ambient temperature. The detailed solvation properties of nitrogen, and especially its selectivity, across a wide range of common target species of extraction still require further investigation. Herein we describe a protocol for the supercritical nitrogen processing of porous magnesium borohydride.

Nitrogen is an effective supercritical fluid for extraction or drying processes due to its small molecular size, high density in the near-liquid supercritical regime, and chemical inertness. We present a supercritical nitrogen drying protocol for the purification treatment of reactive, porous materials.

Supercritical fluid extraction and drying methods are well established in numerous applications for the synthesis and processing of porous materials. ...

Fabrication of Large-area Free-standing Ultrathin Polymer Films

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films. Typically, ultrathin films are prepared using either sacrificial layers, which may damage the film or affect its mechanical properties, or they are made on freshly cleaved mica, a substrate that is difficult to scale. Further, the size of ultrathin film is typically limited to a few square millimeters. In this method, we modify a surface with a polyelectrolyte that alters the strength of adhesion between polymer and deposition substrate. The polyelectrolyte can be shown to remain on the wafer using spectroscopy, and a treated wafer can be used to produce multiple films, indicating that at best minimal amounts of the polyelectrolyte are added to the film. The process has thus far been shown to be limited in scalability only by the size of the coating equipment, and is expected to be readily scalable to industrial processes. In this study, the protocol for making the solutions, preparing the deposition surface, and producing the films is described.

We describe a method for the fabrication of large-area (up to 13 cm diameter) and ultrathin (as thin as 8 nm) polymer films. Instead of using a sacrificial interlayer to delaminate the film from its substrate, we use a self-limiting surface treatment suitable for arbitrarily large areas.

This procedure describes a method for the fabrication of large-area and ultrathin free-standing polymer films.  Typically, ultrathin films are prepared ...

Unraveling Entropic Rate Acceleration Induced by Solvent Dynamics in Membrane Enzymes

Enzyme catalysis evolved in an aqueous environment. The influence of solvent dynamics on catalysis is, however, currently poorly understood and usually neglected. The study of water dynamics in enzymes and the associated thermodynamical consequences is highly complex and has involved computer simulations, nuclear magnetic resonance (NMR) experiments, and calorimetry. Water tunnels that connect the active site with the surrounding solvent are key to solvent displacement and dynamics. The protocol herein allows for the engineering of these motifs for water transport, which affects specificity, activity and thermodynamics. By providing a biophysical framework founded on theory and experiments, the method presented herein can be used by researchers without previous expertise in computer modeling or biophysical chemistry. The method will advance our understanding of enzyme catalysis on the molecular level by measuring the enthalpic and entropic changes associated with catalysis by enzyme variants with obstructed water tunnels. The protocol can be used for the study of membrane-bound enzymes and other complex systems. This will enhance our understanding of the importance of solvent reorganization in catalysis as well as provide new catalytic strategies in protein design and engineering.

Channels for the transportation of water molecules in enzymes influence active site solvation and catalysis. Herein we present a protocol for the engineering of these additional catalytic motifs based on in silico computer modeling and experiments. This will enhance our understanding of the influence of solvent dynamics on enzyme catalysis.

Enzyme catalysis evolved in an aqueous environment. The influence of solvent dynamics on catalysis is, however, currently poorly understood and usually ...

Cooling Rate Dependent Ellipsometry Measurements to Determine the Dynamics of Thin Glassy Films

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements are simple high-throughput characterization experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glassy states for a variety of glassy materials. This technique allows for these parameters to be measured in a single experiment, while other methods must combine a variety of different techniques to investigate all of these properties. Measurements of dynamics close to Tg are particularly challenging. The advantage of cooling rate dependent Tg measurements over other methods which directly probe bulk and surface relaxation dynamics is that they are relatively quick and simple experiments, which do not utilize fluorophores or other complicated experimental techniques. Furthermore, this technique probes the average dynamics of technologically relevant thin films in temperature and relaxation time (&#964;&#945;) regimes relevant to the glass transition (&#964;&#945; &#62; 100 sec). The limitation to using ellipsometry for cooling rate dependent Tg experiments is that it cannot probe relaxation times relevant to measurements of viscosity (&#964;&#945; &#60;&#60; 1 sec). Other cooling rate dependent Tg measurement techniques, however, can extend the CR-Tg method to faster relaxation times. Furthermore, this technique can be used for any glassy system so long as the integrity of the film remains throughout the experiment.

Here, we present a protocol for cooling rate dependent ellipsometry experiments, which can determine the glass transition temperature (Tg), average dynamics, fragility and the expansion coefficient of the super-cooled liquid and glass for a variety of glassy materials.

This report aims to fully describe the experimental technique of using ellipsometry for cooling rate dependent Tg (CR-Tg) experiments. These measurements ...

Preparation of Macroporous Epitaxial Quartz Films on Silicon by Chemical Solution Deposition

This work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step process based on the preparation of a sol in a one-pot synthesis which is followed by the deposition of a gel film on Si(100) substrates by evaporation induced self-assembly using the dip-coating technique and ends with a thermal treatment of the material to induce the gel crystallization and the growth of the quartz film. The formation of a silica gel is based on the reaction of a tetraethyl orthosilicate and water, catalyzed by HCl, in ethanol. However, the solution contains two additional components that are essential for preparing mesoporous epitaxial quartz films from these silica gels dip-coated on Si. Alkaline earth ions, like Sr2+ act as glass melting agents that facilitate the crystallization of silica and in combination with cetyl trimethylammonium bromide (CTAB) amphiphilic template form a phase separation responsible of the macroporosity of the films. The good matching between the quartz and silicon cell parameters is also essential in the stabilization of quartz over other SiO2 polymorphs and is at the origin of the epitaxial growth.

A protocol is presented for the preparation of piezoelectric macroporous epitaxial films of quartz on silicon by solution chemistry using dip-coating and thermal treatments in air.

This work describes the detailed protocol for preparing piezoelectric macroporous epitaxial quartz films on silicon(100) substrates. This is a three-step ...

Dissolution Dynamic Nuclear Polarization Instrumentation for Real-time Enzymatic Reaction Rate Measurements by NMR

The main limitation of NMR-based investigations is low sensitivity. This prompts for long acquisition times, thus preventing real-time NMR measurements of metabolic transformations. Hyperpolarization via dissolution DNP circumvents part of the sensitivity issues thanks to the large out-of-equilibrium nuclear magnetization stemming from the electron-to-nucleus spin polarization transfer. The high NMR signal obtained can be used to monitor chemical reactions in real time. The downside of hyperpolarized NMR resides in the limited time window available for signal acquisition, which is usually on the order of the nuclear spin longitudinal relaxation time constant, T1, or, in favorable cases, on the order of the relaxation time constant associated with the singlet-state of coupled nuclei, TLLS. Cellular uptake of endogenous molecules and metabolic rates can provide essential information on tumor development and drug response. Numerous previous hyperpolarized NMR studies have demonstrated the relevancy of pyruvate as a metabolic substrate for monitoring enzymatic activity in vivo. This work provides a detailed description of the experimental setup and methods required for the study of enzymatic reactions, in particular the pyruvate-to-lactate conversion rate in presence of lactate dehydrogenase (LDH), by hyperpolarized NMR.

The sensitivity enhancement provided by dissolution dynamic nuclear polarization (DNP) enables following metabolic processes in real time by NMR and MRI. The characteristics and performances of a dedicated dissolution DNP setup designed for study enzymatic reactions are discussed.

The main limitation of NMR-based investigations is low sensitivity. This prompts for long acquisition times, thus preventing real-time NMR measurements of ...

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

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

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

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

Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

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

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

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

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven effective in gas adsorption, separations, and catalysis. MOFs are most commonly synthesized as bulk powder, requiring additional processes to adhere them to functional devices and fabrics that risk decreasing the powder porosity and adsorption capacity. Here, we demonstrate a method of first coating fabrics with metal oxide films using atomic layer deposition (ALD). This process creates conformal films of controllable thickness on each fiber, while providing a more reactive surface for MOF nucleation. By submerging the ALD coated fabric in solution during solvothermal MOF synthesis, the MOFs create a conformal, well-adhered coating on the fibers, resulting in a MOF-functionalized fabric, without additional adhesion materials that may block MOF pores and functional sites. Here we demonstrate two solvothermal synthesis methods. First, we form a MIL-96(Al) layer on polypropylene fibers using synthetic conditions that convert the metal oxide to MOF. Using initial inorganic films of varying thicknesses, diffusion of the organic linker into the inorganic allows us to control the extent of MOF loading on the fabric. Second, we perform a solvothermal synthesis of UiO-66-NH2 in which the MOF nucleates on the conformal metal oxide coating on polyamide-6 (PA-6) fibers, thereby producing a uniform and conformal thin film of MOF on the fabric. The resulting materials can be directly incorporated into filter devices or protective clothing and eliminate the maladroit qualities of loose powder.

Solvothermal Synthesis of MIL-96 and UiO-66-NH2 on Atomic Layer Deposited Metal Oxide Coatings on Fiber Mats

Metal-organic frameworks are effective in gas storage and heterogeneous catalysis, but typical synthesis methods result in loose powders that are difficult to incorporate into smart materials. We demonstrate a method of first coating fabrics with ALD metal oxides, resulting in conformal films of MOF on the fabrics during solvothermal synthesis.

Metal-organic frameworks (MOFs), which contain reactive metal clusters and organic ligands allowing for large porosities and surface areas, have proven ...