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 border="0" cellpadding="0" cellspacing="0" style="width:607px;" width="607">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">1ary dry scroll vacuum pump</td>
			<td style="width:89px;">Agilent</td>
			<td style="width:119px;">SH-100</td>
			<td style="width:183px;">All chambers except B1</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">1ary pump</td>
			<td style="width:89px;">EDWARDS</td>
			<td style="width:119px;">nXDS10i 100/240V</td>
			<td>B1 chamber</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Acetone</td>
			<td style="width:89px;"></td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Acquisition programme</td>
			<td colspan="2">Developed in-house</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Analyser</td>
			<td style="width:89px;">Specs</td>
			<td>Phoibos 150 hemispherical&#160;</td>
			<td>A4 chamber</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Argon</td>
			<td style="width:89px;">BASI</td>
			<td style="width:119px;"></td>
			<td>6N</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">Atomic source</td>
			<td style="width:89px;">GenII plasma source</td>
			<td style="width:119px;">Tectra</td>
			<td>B3 chamber</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Au foil</td>
			<td style="width:89px;">Goodfellow</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">CasaXPS programme</td>
			<td style="width:89px;">CasaXPS</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Gauge 1ary vacuum&#160;</td>
			<td style="width:89px;">PFEIFFER</td>
			<td style="width:119px;">TPR 280 (2011/10)</td>
			<td>All chambers</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Gauge 2ary vacuum&#160;</td>
			<td style="width:89px;">VACOM</td>
			<td style="width:119px;">ATMION ATS40C</td>
			<td>All chambers</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hydrogen gas</td>
			<td style="width:89px;">BASI</td>
			<td style="width:119px;"></td>
			<td>6N</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ion gun source</td>
			<td style="width:89px;">Specs</td>
			<td style="width:119px;">IG10/35</td>
			<td>B1 chamber</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Linear transfer programme</td>
			<td style="width:89px;">Specs</td>
			<td style="width:119px;"></td>
			<td>Program delivered with the station</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Origin programme&#160;</td>
			<td style="width:89px;">Origin</td>
			<td style="width:119px;">OriginPro 8.1SRO</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Oxygen gas</td>
			<td style="width:89px;"></td>
			<td style="width:119px;"></td>
			<td>6N</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Sampler e-beam heater power supply</td>
			<td style="width:89px;">Specs</td>
			<td style="width:119px;">SH100</td>
			<td>B1 chamber</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Sampler resistance heater</td>
			<td style="width:89px;">Made in-house</td>
			<td style="width:119px;">power supply + Eurotherm</td>
			<td>B3 chamber</td>
		</tr>
		<tr height="61">
			<td height="61" style="height:61px;width:216px;">Sputtering programme</td>
			<td></td>
			<td></td>
			<td>Developed in-house</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Stainless steal or Molybdenum substrate</td>
			<td style="width:89px;">in house</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Ta wire</td>
			<td style="width:89px;">Goodfellow</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">turbo pump</td>
			<td style="width:89px;">PFEIFFER</td>
			<td style="width:119px;">TC 400</td>
			<td>All chambers&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Uranium target</td>
			<td style="width:89px;">in house</td>
			<td style="width:119px;">in house</td>
			<td style="width:183px;">Natural uranium target</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Vacuum gauge controller</td>
			<td style="width:89px;">VACOM</td>
			<td style="width:119px;">MVC-3</td>
			<td>All chambers</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">X-ray source</td>
			<td style="width:89px;">Specs</td>
			<td style="width:119px;">XRC-1000 MF</td>
			<td style="width:183px;">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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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://www.jove.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

Research

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

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Supercritical Nitrogen Processing for the Purification of Reactive Porous Materials

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

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

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

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 ...

A Method to Manipulate Surface Tension of a Liquid Metal via Surface Oxidation and Reduction

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where interfacial tension is a dominant force. A variety of methods exist for controlling the interfacial tension of aqueous and organic liquids on this scale; however, these techniques have limited utility for liquid metals due to their large interfacial tension.
Liquid metals can form soft, stretchable, and shape-reconfigurable components in electronic and electromagnetic devices. Although it is possible to manipulate these fluids via mechanical methods (e.g., pumping), electrical methods are easier to miniaturize, control, and implement. However, most electrical techniques have their own constraints: electrowetting-on-dielectric requires large (kV) potentials for modest actuation, electrocapillarity can affect relatively small changes in the interfacial tension, and continuous electrowetting is limited to plugs of the liquid metal in capillaries.
Here, we present a method for actuating gallium and gallium-based liquid metal alloys via an electrochemical surface reaction. Controlling the electrochemical potential on the surface of the liquid metal in electrolyte rapidly and reversibly changes the interfacial tension by over two orders of magnitude ( &#820;500 mN/m to near zero). Furthermore, this method requires only a very modest potential (&#60; 1 V) applied relative to a counter electrode. The resulting change in tension is due primarily to the electrochemical deposition of a surface oxide layer, which acts as a surfactant; removal of the oxide increases the interfacial tension, and vice versa. This technique can be applied in a wide variety of electrolytes and is independent of the substrate on which it rests.

We present a method to control the interfacial energy of a liquid metal in an electrolyte via electrochemical deposition (or removal) of a surface oxide layer. This simple method can control the capillary behavior of gallium-based liquid metals by tuning the interfacial energy rapidly, significantly, and reversibly using modest voltages.

Controlling interfacial tension is an effective method for manipulating the shape, position, and flow of fluids at sub-millimeter length scales, where ...

Epitaxial Growth of Perovskite Strontium Titanate on Germanium via Atomic Layer Deposition

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and conformality by taking advantage of self-limiting reactions between vapor-phase precursors and the growing film. Perovskite oxides present potential for next-generation electronic materials, but to-date have mostly been deposited by physical methods. This work outlines a method for depositing SrTiO3 (STO) on germanium using ALD. Germanium has higher carrier mobilities than silicon and therefore offers an alternative semiconductor material with faster device operation. This method takes advantage of the instability of germanium's native oxide by using thermal deoxidation to clean and reconstruct the Ge (001) surface to the 2&#215;1 structure. 2-nm thick, amorphous STO is then deposited by ALD. The STO film is annealed under ultra-high vacuum and crystallizes on the reconstructed Ge surface. Reflection high-energy electron diffraction (RHEED) is used during this annealing step to monitor the STO crystallization. The thin, crystalline layer of STO acts as a template for subsequent growth of STO that is crystalline as-grown, as confirmed by RHEED. In situ X-ray photoelectron spectroscopy is used to verify film stoichiometry before and after the annealing step, as well as after subsequent STO growth. This procedure provides framework for additional perovskite oxides to be deposited on semiconductors via chemical methods in addition to the integration of more sophisticated heterostructures already achievable by physical methods.

This work details the procedures for the growth and characterization of crystalline SrTiO3 directly on germanium substrates by atomic layer deposition. The procedure illustrates the ability of an all-chemical growth method to integrate oxides monolithically onto semiconductors for metal-oxide semiconductor devices.

Atomic layer deposition (ALD) is a commercially utilized deposition method for electronic materials. ALD growth of thin films offers thickness control and ...

A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates.

The study of methods to generate on-demand hydrogen for fuel cells continues to grow in importance. However, systems to measure hydrogen evolution from the reaction of chemicals with water can be complicated and expensive. This article details a simple, low-cost, and robust method to measure the evolution of hydrogen gas.

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) ...

An Optimized Protocol for the Efficient Radiolabeling of Gold Nanoparticles by Using a 125I-labeled Azide Prosthetic Group

Here, we demonstrate a detailed protocol for the radiosynthesis of a 125I-labeled azide prosthetic group and its application to the efficient radiolabeling of DBCO-group-functionalized gold nanoparticles using a copper-free click reaction. Radioiodination of the stannylated precursor (2) was carried out by using [125I]NaI and chloramine T as an oxidant at room temperature for 15 min. After HPLC purification of the crude product, the purified 125I-labeled azide (1) was obtained with high radiochemical yield (75 &plusmn; 10%, n = 8) and excellent radiochemical purity (&gt;99%). For the synthesis of radiolabeled 13-nm-sized gold nanoparticles, the DBCO-functionalized gold nanoparticles (3) were prepared by using a thiolated polyethylene glycol polymer. A copper-free click reaction between 1 and 3 gave the 125I-labeled gold nanoparticles (4) with more than 95% of radiochemical yield as determined by radio-thin-layer chromatography (radio-TLC). These results clearly indicate that the present radiolabeling method using a strain-promoted copper-free click reaction will be useful for the efficient and convenient radiolabeling of DBCO-group-containing nanomaterials.

An Optimized Protocol for the Efficient Radiolabeling of Gold Nanoparticles by Using a 125I-labeled Azide Prosthetic Group

A detailed procedure for the synthesis of a 125I-labeled azide and the radiolabeling of dibenzocyclooctyne (DBCO)-group-conjugated, 13-nm-sized gold nanoparticles using a copper-free click reaction is described.

Here, we demonstrate a detailed protocol for the radiosynthesis of a 125I-labeled azide prosthetic group and its application to the efficient ...

Synthesis of Platinum-nickel Nanowires and Optimization for Oxygen Reduction Performance

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen reduction reaction. Spontaneous galvanic displacement was used to deposit Pt layers onto Ni nanowire substrates. The synthesis approach produced catalysts with high specific activities and high Pt surface areas. Hydrogen annealing improved Pt and Ni mixing and specific activity. Acid leaching was used to preferentially remove Ni near the nanowire surface, and oxygen annealing was used to stabilize near-surface Ni, improving durability and minimizing Ni dissolution. These protocols detail the optimization of each post-synthesis processing step, including hydrogen annealing to 250 &#176;C, exposure to 0.1 M nitric acid, and oxygen annealing to 175 &#176;C. Through these steps, Pt-Ni nanowires produced increased activities more than an order of magnitude than Pt nanoparticles, while offering significant durability improvements. The presented protocols are based on Pt-Ni systems in the development of fuel cell catalysts. These techniques have also been used for a variety of metal combinations, and can be applied to develop catalysts for a number of electrochemical processes.

&#160; The protocol describes the synthesis and electrochemical testing of platinum-nickel nanowires. Nanowires were synthesized by the galvanic displacement of a nickel nanowire template. Post-synthesis processing, including hydrogen annealing, acid leaching, and oxygen annealing were used to optimize nanowire performance and durability in the oxygen reduction reaction.

Platinum-nickel (Pt-Ni) nanowires were developed as fuel cell electrocatalysts, and were optimized for the performance and durability in the oxygen ...

A Rapid Synthesis Method for Au, Pd, and Pt Aerogels Via Direct Solution-Based Reduction

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various precursor noble metal ions with reducing agents in a 1:1 (v/v) ratio results in the formation of metal gels within seconds to minutes compared to much longer synthesis times for other techniques such as sol-gel. Conducting the reduction step in a microcentrifuge tube or small volume conical tube facilitates a proposed nucleation, growth, densification, fusion, equilibration model for gel formation, with final gel geometry smaller than the initial reaction volume. This method takes advantage of the vigorous hydrogen gas evolution as a by-product of the reduction step, and as a consequence of reagent concentrations. The solvent accessible specific surface area is determined with both electrochemical impedance spectroscopy and cyclic voltammetry. After rinsing and freeze drying, the resulting aerogel structure is examined with scanning electron microscopy, X-ray diffractometry, and nitrogen gas adsorption. The synthesis method and characterization techniques result in a close correspondence of aerogel ligament sizes. This synthesis method for noble metal aerogels demonstrates that high specific surface area monoliths may be achieved with a rapid and direct reduction approach.

A rapid, direct solution-based reduction synthesis method to obtain Au, Pd, and Pt aerogels is presented.

Here, a method to synthesize gold, palladium, and platinum aerogels via a rapid, direct solution-based reduction is presented. The combination of various ...

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. ...