The authors have no acknowledgements.

1. Sample Holder Preparation
NOTE: Handling of the sample holder outside of the Labstation under an ambient atmosphere should be performed with gloves and clean tweezers.
<ol>
	<li>Sample holder preparation and ex situ cleaning
	<ol>
		<li>Clean a gold (Au) foil (0.025 mm thickness, 99.99%, see Table of Materials) of size 8 x 8 mm with acetone. Place the foil on a stainless steel or molybdenum holder specifically designed for the Labstation and fix the foil on the holder by spot welding tantalum wires.</li>
		<li>Clean the sample holder and foil again with acetone and let it dry under ambient atmosphere before introduction to the Labstation. 
		NOTE: A photo of the sample holder with a gold foil is displayed in the inset of Figure 1.</li>
	</ol>
	</li>
	<li>Introduction of the sample holder to the Labstation
	<ol>
		<li>Close the UHV valve between the load lock chamber and garage chamber (C1/C2). Untighten the screw, fixing the door of C1, and open the nitrogen valve to bring the pressure to atmospheric pressure, enabling opening of the door.</li>
		<li>Introduce the sample holder to C1. Close the door of C1 and open the valve for the primary vacuum.</li>
		<li>Close the valve to the primary pump once the primary vacuum reaches a pressure of about 1 mbar. Open the valve linked to the UHV turbomolecular pump immediately afterwards.Wait until the pressure reaches 10-7 mbar. 
		NOTE: This last step can take a minimum of 1 to 3 h, depending on sample outgassing.</li>
	</ol>
	</li>
	<li>Transfer to the preparation chamber (B1)
	<ol>
		<li>Move the transport wagon from the transfer chamber to the intermediate chamber and close the valve between C2 and C3. Open the valve located between C1 and C2. Use the transfer rod of C1 to transfer the sample holder to C2. 
		NOTE: C2 is an intermediate chamber between C1 and the linear transfer chamber common to all chambers of the Labstation. It separates the load lock chamber, which has a poor vacuum (10-7 mbar) from the rest of the system (around 10-9 mbar). Sample transfers can be rapidly performed at a relatively poor vacuum in the load lock while keeping the Labstation clean.</li>
		<li>After the sample holder sits on the wagon in C2, bring back the transfer rod to C1 and close the valve between C1 and C2. Open the valve between C2 and the linear transfer chamber C3.</li>
		<li>Position the wagon in the linear transfer chamber and connect it to the driving magnet before closing the valve between C2 and C3.</li>
		<li>Use the program Linear Transfer Control (LTC, Figure 2) to transfer the wagon to the position of the preparation chamber B1.</li>
		<li>Open the valve between the linear transfer chamber and the preparation chamber B1. Use the transfer rod to position the sample in the preparation chamber B1. Once the transfer rod is back to its initial position, close the valve between the linear transfer chamber and preparation chamber B1.</li>
	</ol>
	</li>
	<li>In situ cleaning of the sample holder
	<ol>
		<li>Open the argon valve to reach a pressure of 5 x 10-5 mbar.</li>
		<li>Position the sample holder surface in the vertical to face the ion gun (IG10/35, see Table of Materials).</li>
		<li>Switch on the ion gun to start Ar ion sputtering (2 keV, 10 mA emission current) and keep cleaning for 10 min. Switch off the ion gun.</li>
		<li>Bring the thermocouple in contact with the sample holder, then switch on the e-beam heater to anneal the sample at 773 K for 5 min. After an initial rise (into the 10-7 mbar range), the pressure falls back to about 10-8 mbar, indicating outgassing completion. Switch off the e-beam heater and let the sample cool down to room temperature (RT).</li>
		<li>Open the valve between the preparation chamber B1 and linear transfer chamber, then position the sample holder on the wagon using the transfer rod. Close the valve of the B1 chamber.</li>
	</ol>
	</li>
	<li>Sample holder characterization 
	NOTE: High-resolution X-ray photoelectron spectroscopy (XPS) measurements were performed using a hemispherical analyser (see Table of Materials). A micro-focus source (see Table of Materials) equipped with a monochromator and operating at 120 W was used to produce a radiation of Al K&#945; (E = 1,486.6 eV). Calibration of the spectrometer was done using the 4f7/2 line of an Au metal, producing a value of 83.9(1) eV binding energy (BE), and the 2p3/2 line of a Cu metal at 932.7(1) eV BE.
	<ol>
		<li>Transfer the wagon by remote control using the LTC program to the position of the analysis chamber A4. 
		NOTE: The background pressure in the analysis chamber is 2 x 10&#8722;10 mbar.</li>
		<li>Open the valve of the analyses chamber A4 and use the transfer rod to take the sample from the linear transfer chamber to analyses chamber A4. Close the valve of the analysis chamber A4.</li>
		<li>Transfer the sample to the analysis position using the acquisition program (Figure 3).</li>
		<li>Switch on the cooling water and X-ray source of the spectrophotometer (anode voltage = 15 keV, emission current = 120 mA).</li>
		<li>Start the data acquisition using the acquisition program (Figure 3). 
		NOTE: Optimization of the sample position can be performed with the acquisition program to obtain maximal signal intensity. 
		NOTE: Photoemission spectra were taken from the sample surface kept at RT.</li>
		<li>Start the measurement of an overview spectrum using the following parameters: KEini = 100 eV, KEfin = 1,500 eV, scan time = 300 s, N&#176; of points = 1,401, pass energy = 50 eV, slit = 7 x 20 mm diameter,mode = 1.5 keV/medium area mode. 
		NOTE: The absence of a C1s peak at about 284.5 eV BE indicates that the surface is clean.</li>
		<li>Start the acquisition of Au4f core level spectrum with the following parameters: KEini = 1,396.6 eV, KEfin = 1,406.6 eV, scan time = 60 s, number of points = 201, pass energy = 30 eV, slit = 6 mm diameter, mode = 1.5 keV/medium area mode. 
		NOTE: This latter measurement will be compared to the spectrum after deposition of the UO2 film on the gold foil to evaluate corresponding thickness of the film.</li>
		<li>Once the surface of the sample holder (Au foil) has been analyzed, open the valve of the analysis chamber A4 to position the sample holder on the wagon in the linear transfer chamber using the transfer rod.</li>
	</ol>
	</li>
</ol>
2. Thin Film Preparation
NOTE: Uranium oxide thin films are prepared in situ by direct current (DC) sputtering using a uranium metal target and gas mixture of Ar (6 N) and O2 (4.5 N) partial pressure.
<ol>
	<li>Deposition of UO2 film
	<ol>
		<li>Transfer the wagon carrying the sample holder to the position of the preparation chamber B2 by remote control using the LTC program.</li>
		<li>Open the valve of the preparation chamber B2, and with the transfer rod, position the sample holder under the sputter source, located in the middle of B2. 
		NOTE: Before the sputtering process, ensure that the shutter of the sputter source is closed.</li>
		<li>Close the valve to isolate the B2 chamber from the linear transfer chamber. Then, open the O2 valve and adjust the oxygen partial pressure to 2.5 x 10&#8722;5 mbar. Open the argon valve gas to reach a partial pressure of 5 x 10&#8722;3 mbar.</li>
		<li>Use the sputtering program (Figure 4) to enter the following parameters: deposition time = 300 s, uranium target voltage = -700 V, uranium target current = 2 mA, filament heating = 3.3 V/3.9 A, filament working voltage = 40 V. 
		NOTE: Wait for about 120 s of sputtering with the closed shutter of the sputter source.</li>
		<li>Start the timer immediately after opening the shutter of the sputter source to allow deposition of UO2 on the Au foil. 
		NOTE: To work at low Ar pressure without stabilizing magnetic fields, injections of 25-50 eV energy (triode setup) were enabled to maintain the plasma in the diode.</li>
		<li>Stop the sputtering after 300 s, using the corresponding program, and close the Ar and O2 gas valves. 
		NOTE: The blue light of the plasma will disappear and all sputtering parameters will fall to zero. 
		NOTE: Wait until the pressure of the preparation chamber B2 reaches 10-8 mbar.</li>
		<li>Bring the sample in preparation chamber B1, and for a smooth annealing of the sample, switch on the e-beam heater and set the temperature to 573 K. 
		NOTE: Wait for 3 to 5 min before stopping the heating.</li>
	</ol>
	</li>
	<li>UO2 sample characterisation 
	NOTE: For characterisation of the sample by XPS, the same procedure described for the sample holder characterisation should be followed.
	<ol>
		<li>Open the valve between the preparation chamber B1 and linear transfer chamber to transfer the sample to the wagon using the transfer rod. Set the transfer rod back to the preparation chamber B1, then close the valve to isolate it from the linear transfer chamber.</li>
		<li>Follow the same procedure described in steps 1.5.1 to 1.5.6. 
		NOTE: The overview spectrum enables control of the quality of the UO2 film by excluding additional impurity peaks (C1s, cross-contamination from the sputter source housing) and controlling (roughly) the U:O ratio of the film.</li>
		<li>Start acquisition of the Au4f core level (similar parameters as in step 1.5.7).</li>
		<li>Proceed to the acquisition of U4f, O1s, and valence band (VB) using the following parameters:pass energy = 30 eV, slit = 7 x 20 mm diameter, mode = 1.5 keV, medium area. 
		 
		U4f: KEini = 1,066.6 eV&#160; &#160;KEfin = 1,126.6 eV&#160; &#160; &#160;Scan time = 300 s&#160; &#160; N&#176; of points = 601 
		O1s: KEini = 946.6 eV&#160; &#160;KEfin = 966.6 eV&#160; &#160; &#160;Scan time = 300 s&#160; &#160; N&#176; of points = 201 
		Vb: KEini = 1,473.6 eV&#160; &#160;KEfin = 1,488.6 eV&#160; &#160; &#160;Scan time = 1,800 s&#160; &#160; N&#176; of points = 601 
		 
		NOTE: The obtained spectra for the UO2 film are reported in Figure 5.</li>
	</ol>
	</li>
	<li>Oxidation of UO2 with atomic oxygen 
	NOTE: The atom flux (see Table of Materials) is specified to &#62;1016 atoms/cm2/s, corresponding to an exposure up to 20 s of roughly 10 Langmuirs (i.e., 1.33 x 10&#8722;3 Pa&#8226;s).
	<ol>
		<li>Transfer the wagon carrying the sample to the preparation chamber B3. Open the valve of the preparation chamber B3, and with the transfer rod, position the sample inside B3 in front of the atom source. Close the valve to isolate the chamber from the linear transfer chamber.</li>
		<li>Set the sample temperature to 573 K. Wait 5 min to allow the sample to reach the holder&#39;s temperature.</li>
		<li>Open the oxygen valve and set the partial pressure to 1.2 x 10-5 mbar O2. Switch on the cooling water for the atom source.</li>
		<li>Switch on the atomic source and set the current to 20 mA. Pay attention to the exact time to oxidize the sample with the atomic source. If oxidation time is too short, the oxidation to UO3 can be incomplete as reported in Figure 6.</li>
		<li>Wait 20 min to achieve complete oxidation of UO2 into UO3 and switch off the atomic source before closing the oxygen valve. Once the pressure of the preparation chamber B3 is 10-7 mbar, open the valve to transfer the sample to the wagon present in the linear transfer chamber. Then, close the valve of the preparation chamber B3.</li>
	</ol>
	</li>
	<li>Analysis of UO3 obtained after oxidation of UO2 with atomic oxygen
	<ol>
		<li>Transfer the sample to the analyses chamber following steps 1.5.1 to 1.5.6; then, for the analyses, follow the same procedure as described in step 2.2.4. 
		NOTE: The corresponding spectra of UO3 are reported in Figure 7.</li>
	</ol>
	</li>
	<li>Reduction of UO3 by atomic hydrogen
	<ol>
		<li>To transfer the sample to the preparation chamber B3, follow steps 2.3.1 and 2.3.2.</li>
		<li>Open the hydrogen valve and set the partial pressure to 3 x 10-5 mbar. Switch on the cooling water for the atom source. Switch on the atomic source and set the current to 30 mA.</li>
		<li>Wait for 60 s of reduction time before switching off the atomic source. Pay attention to the exact time taken to reduce the sample with the atomic source. If reduction time is too long, then UO2+x is further reduced to UO2 as reported in Figure 8. If this occurs, the sample must be oxidized again with atomic oxygen (as we did to get UO3), whose corresponding spectra are reported in Figure 9.</li>
	</ol>
	</li>
	<li>Analysis of U2O5 obtained after reduction of UO3 with atomic hydrogen
	<ol>
		<li>Transfer the sample to the analysis chamber following steps 1.5.1 to 1.5.6; then, for the analyses, follow the same procedure as described in step 2.2.4. 
		NOTE: The obtained spectra of U4f, O1s, and the VB are reported in Figure 10. As an example of incomplete reduction to U2O5, similar spectra as shown in Figure 6 are obtained.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Shoesmith, D. W., Sunder, S., Hocking, W. H., Lipkowski, J., Ross, P. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochemistry+of+UO2+nuclear+fuel.">Electrochemistry of UO2 nuclear fuel.</a> Electrochemistry of Novel Materials. , (1994).</li><li>Shoesmith, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fuel+corrosion+processes+under+waste+disposal+conditions.">Fuel corrosion processes under waste disposal conditions.</a> Journal of Nuclear Matter. 282, 1-31 (2000).</li><li>Gouder, T., Shick, A. B., Huber, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surface+interaction+of+PuO2,+UO2+x+and+UO3+with+water+ice.">Surface interaction of PuO2, UO2+x and UO3 with water ice.</a> Topics in Catalysis. 56, 1112-1120 (2013).</li><li>Cohen, C., 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=Water+chemisorption+on+a+sputter+deposited+uranium+dioxide+film+-+Effect+of+defects.">Water chemisorption on a sputter deposited uranium dioxide film - Effect of defects.</a> Solid State Ionics. 263, 39-45 (2014).</li><li>Seibert, 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=The+use+of+the+electrochemical+quartz+crystal+microbalance+(EQCM)+in+corrosion+studies+of+UO2+thin+film+models.">The use of the electrochemical quartz crystal microbalance (EQCM) in corrosion studies of UO2 thin film models.</a> Journal of Nuclear Matter. 419, 112-121 (2011).</li><li>Majumder, I., 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=Syntheses+of+U3O8+nanoparticles+form+four+different+uranyl+complexes:+Their+catalytic+performance+for+various+alcohol+oxidations.">Syntheses of U3O8 nanoparticles form four different uranyl complexes: Their catalytic performance for various alcohol oxidations.</a> Inorganic Chimica Acta. 462, 112-122 (2017).</li><li>Gouder, T., 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=Direct+observation+of+pure+pentavalent+uranium+in+U2O5+thin+films+by+high-resolution+photoemission+spectroscopy.">Direct observation of pure pentavalent uranium in U2O5 thin films by high-resolution photoemission spectroscopy.</a> Scientific Reports. 8, 1-7 (2018).</li><li>Rundle, R. E., Baeziger, N. C., Wilson, A. S., MacDonald, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+structures+of+the+carbides,+nitrides+and+oxides+of+uranium.">The structures of the carbides, nitrides and oxides of uranium.</a> Journal of the American Chemical Society. 70, 99 (1948).</li><li>Hoekstra, H. R., Siegel, S., Gallagher, F. X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+uranium-oxygen+system+at+high+pressure.">The uranium-oxygen system at high pressure.</a> Journal of Inorganic and Nuclear Chemistry. 32, 3237 (1970).</li><li>Kovba, L. M., Komarevtseva, N. I., Kuz'mitcheva, E. U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+the+crystal+structures+of+U13O34+and+delta-U2O5.">On the crystal structures of U13O34 and delta-U2O5.</a> Radiokhimiya. 21, 754 (1979).</li><li>Teterin, Y. 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=A+study+of+synthetic+and+natural+uranium+oxides+by+X-ray+photoelectron+spectroscopy.">A study of synthetic and natural uranium oxides by X-ray photoelectron spectroscopy.</a> Physics and Chemistry of Minerals. 7, 151-158 (1981).</li></ol>

The authors have nothing to disclose.

The initial results obtained on the thin films of U2O5 of about 30 monolayers (ML) in thickness, together with the corresponding core level spectroscopy obtained with high-resolution X-ray photoemission spectroscopy, have been reported in a previous publication7. The evolution of the uranium state during the oxidation process of UO2 into UO3 was reported through X-ray photoelectron spectra obtained on thin films of two to 50 layers in thickness in a wide range of the O:U ratio (Figure 11, Figure 12). Film oxidation and film reduction were obtained by exposing the films to atomic oxygen and atomic hydrogen, respectively. The homogeneity of the films with uranium oxidation states from IV to VI could be confirmed due to their small thickness and the reaction temperatures. Thin films of uranium oxides are deposited on a substrate using direct current sputtering with a sputter source developed at JRC Karlsruhe. The sputter source is installed in a chamber kept under ultra-high vacuum, like all the chambers of the Labstation. While UO2 can be obtained directly, UO3 and U2O5 films are only obtained after further treatment with atomic oxygen and atomic hydrogen. The binding energy of the main peaks and their satellites positions allow differentiation between the oxidation states of uranium in uranium oxide films produced in situ. High-resolution spectroscopy is necessary to differentiate the different oxidation states, as the satellite binding energies are close and have low intensities.
In 1948, pure pentavalent uranium, U2O5, was identified for the first time8. Later, its synthesis was described based on high temperature (673-1,073 K) and high pressure (30-60 kbar) of a mixture of UO2 and U3O89. However, the existence and stability of U2O5 at ambient temperature and pressure conditions have been questioned, suggesting a lower limit of x = 0.56-0.6 for the single-phase region below U3O810. So far, preparation of U2O5 at high pressure and temperature or during a thermo-reduction process was not reproducible; often, it was not possible to assign a single oxidation state to obtained samples. Some of a U2O5 bulk sample preparation appeared as mixtures of UO2 or UO3 with coexistence of U(V) with U(IV) or U(VI), as for U4O9 and U3O8. For instance, Teterin et al.11 reported the leaching process of U3O8 in sulphuric acid followed by thermal treatment in a helium atmosphere, claiming that the results were related to U2O5. This conclusion could be easily excluded due to a resulting two-peak structure in their XPS spectra. A mixture of U(V) and U(VI) species could explain the result, excluding the formation of a single U(V) oxidation state expected for U2O5.
Our method of preparation allows preparation of thin films of uranium oxide with single oxidation states of U(IV), U(VI), and U(V). The entire process of sample preparation takes place in situ within an instrument maintained at ultra-high vacuum. It was found that reduction of UO3 by atomic hydrogen does not proceed to UO2 but can be stopped at U(V). The time factor is very important as well as the temperature of the sample during the reduction process. With the high-resolution photoemission spectrometer, it was shown that a pure sample of U2O5 can be prepared in situ. Preparing thicker films should be a next step in looking at the crystallographic structure and bulk properties with ex situ techniques.

Uranium oxide is the main component of nuclear waste, and its solubility in water is linked to uranium oxidation state, increasing from U(IV) to U(VI). Thus, UO2+x oxidation during geological storage is an important and crucial safety issue1,2. This motivates studies of reaction mechanisms governing the surface interactions between uranium oxides and the environment3,4,5,6. This knowledge is essential to all aspects of treating waste from nuclear fuel cycles.
While tetravalent and hexavalent uranium are well-established and common as solid-state systems, this is not the case for pentavalent uranium, despite its stability in uranyl complexes and occurrence in aqueous solution. In uranium oxides, U(V) is considered a metastable intermediate, and it is not reported as single-state but rather as coexisting with U(IV) and U(VI) species. For this reason, nothing has been reported about the chemical and physical properties of U2O5. This is also due to a common feature of corrosion experiments, in which samples are exposed to a corrosive environment. This creates a steep gradient in oxidation states between the surface (exposed to the oxidants) and bulk of the sample. The change takes place within the analysis depth. Thus, different oxidation states are observed simultaneously, not because of mixed valence, but as an artefact of an incomplete reaction resulting in a heterogeneous layer. These two problems can be resolved by using thin films instead of bulk samples. Large numbers of diverse systems can be prepared with little starting material, and the surface-bulk gradient is avoided because there is no bulk.
The method reported here allows in situ preparation of a very thin layer (some tens of atomic layers deposited on an inert substrate) and analysis of its surface without contact with the atmosphere. This is one of the advantages of the Labstation (Figure 1), which is a modular machine composed of different chambers kept under dynamic ultra-high vacuum (UHV), reaching pressures of 10-9-10-11 mbar. Chambers are dedicated to preparation of the thin films, surface treatment (gas adsorptions), and characterisation by surface spectroscopies techniques [e.g., x-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS), low energy electron diffraction spectroscopy (LEED)]. Samples are mounted on specific sample holders and transferred between different chambers through a linear transfer chamber using a transport wagon. All chambers are connected to this central chamber through a valve so they can be isolated at any moment (e.g., for gas filling or servicing). Recuperation of the sample holder/sample from the linear transfer chamber is accomplished by a transfer rod mounted on each chamber. The Labstation base system has been manufactured by an external company (see Table of Materials). Extensions and modifications have been added afterwards depending on experimental requirements, resulting in a unique equipment at JRC Karlsruhe. Extensions include the sputter source (a core element for thin film preparation), which has been developed in-house along with the sputter and data acquisition programs. The loading of the sample holder/sample from an ambient atmosphere to ultra-high vacuum is done via a load lock chamber specially designed to perform multiple sample handling and minimize the time to reaching the final pressure of about 10-8-10-9 mbar, thus limiting air contamination of the system. The Labstation is the result of years of experience and expertise in the surface science field at JRC Karlsruhe.
To pass from one chamber to another, the sample is mounted on a transport wagon driven by an external magnet, controlled by a computer program (Figure 2) and moving along the linear transfer chamber of about 7 m to predefined stop positions in front of the chambers.
Without a similar or close installation, the experiment might be difficult to reproduce. However, this installation contributes to the PAMEC laboratory that contributes to the open access program at JRC, in which external users are invited to submit proposals reviewed by a panel of international scientific experts. Their evaluation then allows users to access the infrastructure operated by the JRC. After requests and in the frame of collaborations, thin films can be prepared for external users for analyses and experiments performed outside JRC Karlsruhe.
In this report, we provide a detailed protocol of the growth of single-valence U2O5 thin films, obtained by successive steps involving oxidation and reduction of UO2 with atomic oxygen and atomic hydrogen, respectively. Unlike UO2 and UO2+x, direct deposition of U2O5 and UO3 films by DC sputtering cannot be done. Therefore, we first proceed to the deposition of a UO2 film, oxidize it into UO3 using atomic oxygen, then reduce it back to U2O5 with atomic hydrogen. The oxidation and reduction times and sample temperature during the process have effects on the result and are important to master. Correct composition was verified with high-resolution X-ray photoelectron spectroscopy, which provides direct and quantitative evidence for uranium 5f1 electronic configuration, as expected for the U(V).

<table><tbody><tr><td>1ary dry scroll vacuum pump</td><td>Agilent</td><td>SH-100</td><td>All chambers except B1</td></tr><tr><td>1ary pump</td><td>EDWARDS</td><td>nXDS10i 100/240V</td><td>B1 chamber</td></tr><tr><td>Acetone</td><td></td><td></td><td></td></tr><tr><td>Acquisition programme</td><td>Developed in-house</td><td></td><td></td></tr><tr><td>Analyser</td><td>Specs</td><td>Phoibos 150 hemispherical&amp;nbsp;</td><td>A4 chamber</td></tr><tr><td>Argon</td><td>BASI</td><td></td><td>6N</td></tr><tr><td>Atomic source</td><td>GenII plasma source</td><td>Tectra</td><td>B3 chamber</td></tr><tr><td>Au foil</td><td>Goodfellow</td><td></td><td></td></tr><tr><td>CasaXPS programme</td><td>CasaXPS</td><td></td><td></td></tr><tr><td>Gauge 1ary vacuum&amp;nbsp;</td><td>PFEIFFER</td><td>TPR 280 (2011/10)</td><td>All chambers</td></tr><tr><td>Gauge 2ary vacuum&amp;nbsp;</td><td>VACOM</td><td>ATMION ATS40C</td><td>All chambers</td></tr><tr><td>Hydrogen gas</td><td>BASI</td><td></td><td>6N</td></tr><tr><td>Ion gun source</td><td>Specs</td><td>IG10/35</td><td>B1 chamber</td></tr><tr><td>Linear transfer programme</td><td>Specs</td><td></td><td>Program delivered with the station</td></tr><tr><td>Origin programme&amp;nbsp;</td><td>Origin</td><td>OriginPro 8.1SRO</td><td></td></tr><tr><td>Oxygen gas</td><td></td><td></td><td>6N</td></tr><tr><td>Sampler e-beam heater power supply</td><td>Specs</td><td>SH100</td><td>B1 chamber</td></tr><tr><td>Sampler resistance heater</td><td>Made in-house</td><td>power supply + Eurotherm</td><td>B3 chamber</td></tr><tr><td>Sputtering programme</td><td></td><td></td><td>Developed in-house</td></tr><tr><td>Stainless steal or Molybdenum substrate</td><td>in house</td><td></td><td></td></tr><tr><td>Ta wire</td><td>Goodfellow</td><td></td><td></td></tr><tr><td>turbo pump</td><td>PFEIFFER</td><td>TC 400</td><td>All chambers&amp;nbsp;</td></tr><tr><td>Uranium target</td><td>in house</td><td>in house</td><td>Natural uranium target</td></tr><tr><td>Vacuum gauge controller</td><td>VACOM</td><td>MVC-3</td><td>All chambers</td></tr><tr><td>X-ray source</td><td>Specs</td><td>XRC-1000 MF</td><td>Equipped with a monochromator</td></tr></tbody></table>

u2o5 film preparation via uo2 deposition by direct current sputtering and successive oxidation and reduction with atomic oxygen and atomic hydrogen

We describe a method to produce U2O5 films in situ using the Labstation, a modular machine developed at JRC Karlsruhe. The Labstation, an essential part of the Properties of Actinides under Extreme Conditions laboratory (PAMEC), allows the preparation of films and studies of sample surfaces using surface analytical techniques such as X-ray and ultra-violet photoemission spectroscopy (XPS and UPS, respectively). All studies are made in situ, and the films, transferred under ultra-high vacuum from their preparation to an analyses chamber, are never in contact with the atmosphere. Initially, a film of UO2 is prepared by direct current (DC) sputter deposition on a gold (Au) foil then oxidized by atomic oxygen to produce a UO3 film. This latter is then reduced with atomic hydrogen to U2O5. Analyses are performed after each step involving oxidation and reduction, using high-resolution photoelectron spectroscopy to examine the oxidation state of uranium. Indeed, the oxidation and reduction times and corresponding temperature of the substrate during this process have severe effects on the resulting oxidation state of the uranium. Stopping the reduction of UO3 to U2O5 with single U(V) is quite challenging; first, uranium-oxygen systems exist in numerous intermediate phases. Second, differentiation of the oxidation states of uranium is mainly based on satellite peaks, whose intensity peaks are weak. Also, experimenters should be aware that X-ray spectroscopy (XPS) is a technique with an atomic sensitivity of 1% to 5%. Thus, it is important to obtain a complete picture of the uranium oxidation state with the entire spectra obtained on U4f, O1s, and the valence band (VB). Programs used in the Labstation include a linear transfer program developed by an outside company (see Table of Materials) as well as data acquisition and sputter source programs, both developed in-house.

The identification of U(V) can be easily done by a characteristic energy of the shake-up satellite accompanying the characteristic U4f doublet. The binding energy at which appears the satellite, associated with intrinsic energy loss processes, depends on the uranium oxidation state.
Uranium 4f core level X-ray photoemission spectra are recorded for U(IV) in UO2 (red curve), U(V) in U2O5 (green curve), and U(VI) in UO3 (pink curve), then compared to U(0) in uranium metal (black curve) in the left part of Figure 11. The corresponding O1s core level spectra are superposed and reported in the right part of Figure 11.
In the center part of Figure 11, the U4f7/2 core level peaks have been shifted to superpose the main lines (upper half), allowing visualization of the energy separation (&#916;E) between the satellite and main line (lower half). With increasing oxidation state, the energy separation increases, while satellite intensity decreases. Spectra were obtained on thin films of about 20 monolayers in thickness. The satellite energy peak and the 4f5/2 (4f7/2) emission line were used as a fingerprint for the oxidation state of the uranium atoms. The valence band spectra of UO2, U2O5, and UO3 obtained on the same films are reported in Figure 12.
The spectra described in the protocol are corresponding to UO2 films (Figure 5) obtained after deposition in the preparation chamber B2. This film is then oxidized with atomic oxygen. Depending on the oxidation time, the result can be UO2+x (as reported in Figure 6) or UO3 (as reported in Figure 7). Also, if atomic reduction with hydrogen on UO3 is too long, it will return to UO2 as reported in Figure 8. In this case, reoxidation to UO3 as reported in Figure 9 should take place before reducing it again with an appropriate time to get U2O5, as displayed in Figure 10. The results show that the oxidation and reduction processes are completely reversible.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59017/59017fig1.jpg" /> 
Figure 1: Photograph and schematic of the Labstation machine developed at JRC Karlsruhe to enable in situ surface science studies. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59017/59017fig2.jpg" /> 
Figure 2: Screenshot of the linear transfer control program. The program enables transfer of the wagon carrying the samples (I to V) along the linear transfer chamber at different chamber positions. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59017/59017fig3.jpg" /> 
Figure 3: Screenshot of the acquisition program. Once the measurement conditions are introduced, a series of measurements can be performed automatically after switching on the X-ray generator. The sample position window enables positioning of the sample in the analyses chamber. The adjustment along x, y, and z can be done to optimize the intensity of the signal. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/59017/59017fig4.jpg" /> 
Figure 4: Screenshot of the sputter control program. The sputtering conditions can be selected with this program developed in-house. Among the variables to be defined are the heating and working voltages of the filament and the voltages of up to two targets. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/59017/59017fig5.jpg" /> 
Figure 5: U4f, O1s, and valence band spectra after deposition of a UO2 film, measured by high-resolution X-ray photoemission spectroscopy. The peak and satellite positions are characteristic of a UO2 sample. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/59017/59017fig6.jpg" /> 
Figure 6: U4f, O1s, and valence band spectra after oxidation of UO2 with atomic oxygen, measured by high-resolution X-ray photoemission spectroscopy. The oxidation time is too short, thus the oxidation to UO3 is incomplete. The satellite and peak positions are characteristic of UO2+x and not of the UO3 reported in Figure 7. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/59017/59017fig7.jpg" /> 
Figure 7: U4f, O1s, and valence band spectra measured after oxidation of UO2 film with atomic oxygen using high-resolution X-ray photoemission spectroscopy. The peak and satellite positions are characteristic of a UO3 sample. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/59017/59017fig8.jpg" /> 
Figure 8: U4f, O1s, and valence band spectra measured after reduction of UO3 with atomic hydrogen. The reduction time is too long, thus the U2O5 is further reduced to UO2. The satellite and peak positions are characteristic of a UO2 and not the U2O5 sample reported in Figure 10. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/59017/59017fig9.jpg" /> 
Figure 9: U4f, O1s, and valence band of the sample obtained in Figure 8 and re-oxidized with atomic oxygen to UO3. The satellite and peak positions are characteristic of a UO3 sample. The processes of reduction and oxidation are thus reversible. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig9large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/59017/59017fig10.jpg" /> 
Figure 10: U4f, O1s, and valence band spectra after reduction of UO3 film with atomic hydrogen, measured by high-resolution X-ray photoemission spectroscopy. The peak and satellite positions are characteristic of a U2O5 sample. <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/59017/59017fig11.jpg" /> 
Figure 11: U4f and O1s core level X-ray photoemission spectra of U(IV) in UO2 (red curve), U(V) in U2O5 (green curve), and U(VI) in UO3 (pink curve), then compared to U(0) in uranium metal (black curve). <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig11large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 12" class="xfigimg" src="/files/ftp_upload/59017/59017fig12.jpg" /> 
Figure 12: Valence band spectra of U(IV) in UO2 (red curve), U(V) in U2O5 (black curve), and U(VI) in UO3 (pink curve). <a href="https://jove.unicartagenaproxy.elogim.com/files/ftp_upload/59017/59017fig12large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen at JoVE.co

U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

This protocol presents the preparation of U2O5 thin films obtained in situ under ultra-high vacuum. The process involves oxidation and reduction of UO2 films with atomic oxygen and atomic hydrogen, respectively.

U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

We describe a method to produce U2O5 films in situ using the Labstation, a modular machine developed at JRC Karlsruhe. The Labstation, an essential part ...

u2o5-film-preparation-via-uo2-deposition-direct-current-sputtering

Universidad de Cartagena UDEC

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JoVE Journal

Chemistry

7.9K Views.  Directorate for Nuclear Safety and Security. This protocol presents the preparation of U2O5 thin films obtained in situ under ultra-high vacuum. The process involves oxidation and reduction of UO2 films with atomic oxygen and atomic hydrogen, respectively.

Video: U2O5 Film Preparation via UO2 Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Engineering

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 ...

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O substrates outside vacuum at low temperature. The performance of photovoltaic devices featuring atmospherically fabricated ZnO/Cu2O heterojunction was dependent on the conditions of AP-SALD film deposition, namely, the substrate temperature and deposition time, as well as on the Cu2O substrate exposure to oxidizing agents prior to and during the ZnO deposition. Superficial Cu2O to CuO oxidation was identified as a limiting factor to heterojunction quality due to recombination at the ZnO/Cu2O interface. Optimization of AP-SALD conditions as well as keeping Cu2O away from air and moisture in order to minimize Cu2O surface oxidation led to improved device performance. A three-fold increase in the open-circuit voltage (up to 0.65 V) and a two-fold increase in the short-circuit current density produced solar cells with a record 2.2% power conversion efficiency (PCE). This PCE is the highest reported for a Zn1-xMgxO/Cu2O heterojunction formed outside vacuum, which highlights atmospheric pressure spatial ALD as a promising technique for inexpensive and scalable fabrication of Cu2O-based photovoltaics.

Improved Heterojunction Quality in Cu2O-based Solar Cells Through the Optimization of Atmospheric Pressure Spatial Atomic Layer Deposited Zn1-xMgxO

Here we present a protocol for synthesizing Zn1-xMgxO/Cu2O heterojunctions in open-air at low temperature via atmospheric pressure spatial atomic layer deposition (AP-SALD) of Zn1-xMgxO on cuprous oxide. Such high quality conformal metal oxides can be grown on a variety of substrates including plastics by this cheap and scalable method.

Atmospheric pressure spatial atomic layer deposition (AP-SALD) was used to deposit n-type ZnO and Zn1-xMgxO thin films onto p-type thermally oxidized Cu2O ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

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 ...

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

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

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

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

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 ...

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.

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 ...

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.

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 ...

Tuning Oxide Properties by Oxygen Vacancy Control During Growth and Annealing

Electrical, optical, and magnetic properties of oxide materials can often be controlled by varying the oxygen content. Here we outline two approaches for varying the oxygen content and provide concrete examples for tuning the electrical properties of SrTiO3-based heterostructures. In the first approach, the oxygen content is controlled by varying the deposition parameters during a pulsed laser deposition. In the second approach, the oxygen content is tuned by subjecting the samples to annealing in oxygen at elevated temperatures after the film growth. The approaches can be used for a wide range of oxides and nonoxide materials where the properties are sensitive to a change in the oxidation state.
The approaches differ significantly from electrostatic gating, which is often used to change the electronic properties of confined electronic systems such as those observed in SrTiO3-based heterostructures. By controlling the oxygen vacancy concentration, we are able to control the carrier density over many orders of magnitude, even in nonconfined electronic systems. Moreover, properties can be controlled, which are not sensitive to the density of itinerant electrons.

Oxide materials show many exotic properties that can be controlled by tuning the oxygen content. Here, we demonstrate the tuning of oxygen content in oxides by varying the pulsed laser deposition parameters and by performing postannealing. As an example, electronic properties of SrTiO3-based heterostructures are tuned by growth modifications and annealing.

Electrical, optical, and magnetic properties of oxide materials can often be controlled by varying the oxygen content. Here we outline two approaches for ...

U₂O₅ Film Preparation via UO₂Deposition by Direct Current Sputtering and Successive Oxidation and Reduction with Atomic Oxygen and Atomic Hydrogen

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