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 with deionized (DI) water. 
	CAUTION: Hydrogen gas in abundance is generated from zinc and HCl reaction.</li>
	<li>Remove the tape and wash with DI water and soap using a small brush. 
	NOTE: The brush helps to remove some residual glue from the tape.</li>
	<li>Leave the etched substrate in a soap solution (50% in water) and keep it for 15 min in an ultrasonicate bath. Then, sonicate for 15 min in DI water (2 times), followed by 10 more min in acetone and finally 10 min in isopropyl alcohol. Dry the substrate with nitrogen gas.</li>
</ol>
2. Deposition of niobium oxide films
<ol>
	<li>Fix the substrate through a shadow mask protecting 0.5 cm of both sides. 
	NOTE: On the side where the FTO was etched, it is important to certify that the FTO is covered in order to prevent short circuits when building the cell.</li>
	<li>Introduce the substrate into the sputtering chamber and seal the chamber.</li>
	<li>Start the mechanic pump. In the first 10 min, change the 3-way valve into roughing position to heat its oil and release water to improve the pumping. The primary pump works alone until the pressure is 6 x 10-2 Torr.</li>
	<li>Change the 3-way valve to backing position, and turn the turbo molecular pump on. Once the molecular pump is started, open the gate valve at the vacuum pump entry. Deposition starts when the pressure reaches 3 x 10-6 torr. 
	NOTE: Before starting the molecular pump, the primary vacuum should be better than 6 x 10-2 torr, however, not higher than 5 x 10-2 torr in order to prevent contaminating the chamber with pump oil.</li>
	<li>When the vacuum reaches 5 x 10-5 torr, open the water cooler system and turn on the substrate heating system. Set the temperature at 500 &#176;C. Increase the temperature slowly, 100 &#176;C every 5 min until it reaches the desired value.</li>
	<li>Set the gases parameters to be used in the deposition: argon of 40 sccm and oxygen of 3 to 10 sccm. 
	NOTE: The oxygen flow rate was varied in each deposition: 3, 3.5, 4 and 10 sccm. Oxygen reacts with niobium forming niobium oxide.</li>
	<li>Introduce argon onto the chamber, and set the pressure to 5 x 10-3 torr and the radio frequency (RF) to 120 W. Turn the RF on and tune using the impedance matching box. In case the plasma does not start, increase the pressure slowly until it reaches 2 x 10-2 Torr. In this pressure, the plasma should start. Set the pressure using a gate valve that can be opened or closed to change the pumping rate.</li>
	<li>Keep the plasma at 120 W for 10 min to clean the niobium target removing any oxide layer present in its surface. 
	NOTE: While cleaning the target, the substrate shutter is kept closed to protect the substrate from any material deposition.</li>
	<li>Introduce oxygen into the chamber,&#160;after stabilization, set the radio frequency power to 240 W and&#160;open the substrate shutter. Deposition starts. Set the deposition time to have a final thickness of 100 nm based on previous studies that determined the deposition rate. For each deposition condition a different deposition rate is expected, so the deposition time does also differ.</li>
	<li>Once the deposition time is completed, close the shutter immediately, turn the RF off, the close the gases and decrease the substrate temperature to room temperature.</li>
	<li>As the substrate temperature reaches room temperature, introduce air to reestablish the ambient pressure and open the chamber.. 
	NOTE: Generally, the system takes 4 h to reach a temperature of 40 &#176;C.</li>
</ol>
3. Constructing the solar cells
<ol>
	<li>Preparing the solutions used to construct the devices
	<ol>
		<li>TiO2 paste solution: Mix 150 mg of TiO2 paste in 1 mL of DI water. Stir it for 1 day before use. 
		NOTE: Keep the suspension stirring even when you are not using it to be sure that the suspension is always homogeneous.</li>
		<li>Prepare the lead iodide solution (PbI2) by mixing 420 mg of PbI2 in 1 mL of anhydrous dimethylformamide. Use only anhydrous solvents.</li>
		<li>Prepare the methylammonium iodide (CH3NH3I) solution by adding 8 mg of CH3NH3I in 1 mL of isopropyl alcohol (IPA). 
		NOTE: The water content in IPA must be less than 0.0005%.</li>
	</ol>
	</li>
	<li>Deposit TiO2 mesoporous layer on top of the niobium oxide layer using a spin coater at 4,000 rpm for 30 s.</li>
	<li>Put the substrate on the oven following the steps: 270 &#176;C for 30 min; 370 &#176;C for 30 min and 500 &#176;C for 1 h. Wait until the oven reaches room temperature and remove the substrate. 
	NOTE: The heat treatment decomposes the organic part of the paste leaving a porous layer over the film.</li>
	<li>Deposit two layers of PbI2 on top of the TiO2 mesoporous using a spin coater at 6,000 rpm for 90 s and after each deposition put the substrate in a hot plate at 70 &#176;C for 10 min. 
	NOTE: The PbI2 deposition must be inside a glove box filled with pure nitrogen or argon and with controlled atmosphere (water and oxygen &#60; 0.1 ppm).</li>
	<li>Deposit the CH3NH3I solution. Drop 0.3 mL of CH3NH3I solution onto PbI2, wait 20 s and then spin at 4,000 rpm for 30 s. Put the substrate on a hot plate at 100 &#176;C for 10 min. 
	NOTE: The CH3NH3I deposition must be inside a glove box. The total amount of CH3NH3I solution must be dropped quickly in only one step.</li>
	<li>Deposit Spiro-OMeTAD solution on top of the perovskite layer by spin coating at 4,000 rpm for 30 s. Leave the substrate in an oxygen atmosphere overnight. 
	NOTE: The Spiro-OMeTAD deposition must be inside of a glove box. After the deposition, it is important to leave the substrate overnight in an oxygen atmosphere in order to oxidize the Spiro- OMeTAD increasing its conductivity.</li>
	<li>Evaporate 70 nm of gold contact using a shadow mask at a rate of 0.2 A/s until 5 nm is reached and then increase the rate to 1 A/s. 
	NOTE: It is important to use a slow rate at the beginning to prevent gold diffusion through the cell.</li>
</ol>

<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 authors have nothing to disclose.

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 ...

niobium-oxide-films-deposited-reactive-sputtering-effect-oxygen-flow

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7.2K Views.  Federal University of São Carlos (UFSCAR). 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.

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

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 ...

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 ...

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. ...