Ru 4d Research Articles

Quantitative analysis of trace levels of surface contamination by X‐ray photoelectron spectroscopy. Part II: Systematic uncertainties and absolute quantification

We discuss analyses of trace levels of surface contamination using X‐ray photoelectron spectroscopy (XPS). The problem of quantifying common sources of statistical and systematic uncertainties for these measurements is formulated in terms of the needs of extreme ultraviolet lithography, but the results and conclusions are applicable to a broad range of XPS applications. We quantify the systematic uncertainties introduced by particular cases of overlapping peaks on different substrate structures by simulating measured spectra with the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis (SESSA). One example demonstrates that the relative atomic concentrations of trace elements such as S, P, and halogens on a Ru surface could be dramatically overestimated if the fitting of the overlapping Ru 3d and C 1s peaks excludes the contribution from carbon. We also show how spectra generated by SESSA can be compared with measured spectra to determine absolute amounts of surface impurities on layered samples of the type used for extreme ultraviolet lithography. We provide estimates of the total uncertainty for such measurements by considering the systematic limitations of SESSA and the statistical uncertainties of the measurements. The same procedure can be employed for other multilayered materials. Finally, we describe two approaches for converting XPS detection limits for an elemental impurity in an elemental matrix to the corresponding detection limits for the impurity as a thin film on the surface of the matrix material.

High-Performance Pyrochlore-Type Yttrium Ruthenate Electrocatalyst for Oxygen Evolution Reaction in Acidic Media.

Development of acid-stable electrocatalysts with low overpotential for oxygen evolution reaction (OER) is a major challenge to produce hydrogen directly from water. We report in this paper a pyrochlore yttrium ruthenate (Y2Ru2O7-δ) electrocatalyst that has significantly enhanced performance toward OER in acid media over the best-known catalysts, with an onset overpotential of 190 mV and high stability in 0.1 M perchloric acid solution. X-ray absorption near-edge structure (XANES) indicates Y2Ru2O7-δ electrocatalyst had a low valence state that favors the high OER activity. Density functional theory (DFT) calculation shows this pyrochlore has lower band center energy for the overlap between Ru 4d and O 2p orbitals and is therefore more stable Ru-O bond than RuO2, highlighting the effect of yttrium on the enhancement in stability. The Y2Ru2O7-δ pyrochlore is also free of expensive iridium metal and thus is a cost-effective candidate for practical applications.

Element Strategy Using Ru-Mn Substitution in CuO-CaCu3Ru4O12 Composite Ceramics with High Electrical Conductivity

CaCu3Ru4−xMnxO12 bulks with various substitution amounts x and sintering additive CuO (20 vol.%) were prepared, and the influence of x on the electrical conductivity in a wide temperature range (8–900 K) was investigated. Microstructural observations showed an enhancement of bulk densification upon Mn substitution. Although the resistivity increased with increasing x, the resistivity was as low as a few mΩcm even in the sample with x = 2.00, where half of Ru is substituted by Mn. This high conductivity despite the loss of Ru 4d conduction following the substitution is explained by the A-site (Cu2+) conduction in CaCu3Ru4−xMnxO12. The thermopower of CaCu3Ru4−xMnxO12 was found to be influenced by the substitution, and a sign inversion was observed in the substituted samples at low temperature. The partial substitution of Ru by Mn in CaCu3Ru4O12 enables the reduction of the materials cost while maintaining good electrical conductivity for applications as a conducting device component.

Negligible spin-orbit coupling effect in the Mott-insulating antiferromagnet KRuO4

A comprehensive investigation of the electronic and magnetic properties of KRuO4 has been performed using the first-principles calculations in order to clarify the importance of Coulomb interaction and spin-orbit coupling effect. The results indicate that its ground state is of a G-type Mott-insulating antiferromagnet with nearest-neighbor antiferromagnetic coupling, and the computed magnetic moment of Ru7+ ion is 0.50 μB, in nice agreement with the observed value of 0.57(7) μB. In addition, the electronic structure near the Fermi level is dominated by strong hybridized Ru 4d and O 2p states. In sharply contrast with KOsO4, the significantly weaker spin orbit coupling of Ru 4d electrons has negligible impact on the electronic and magnetic properties of KRuO4, and the orbital contribution to the total moment is minor. On the other hand, the on-site Coulomb repulsion affects the band structure significantly, and is indispensable for appraising the electronic properties, opening the band gap, establishing the orbital ordering of the quarter-filled eg manifold.

Magnetic interactions in praseodymium ruthenate Pr3RuO7 with fluorite-related structure

Solid solutions Pr3(Ru1-xTax)O7 (0≤x≤1.0) and (Pr1-xYx)3RuO7 (0≤x≤0.7) were obtained as a single phase compound. They crystallize in an orthorhombic superstructure derived from that of the cubic fluorite with space group Cmcm. The results of the Rietveld analysis for X-ray diffraction profiles of Pr3(Ru1-xTax)O7 showed that Ru and Ta atoms are randomly situated at the six-coordinate 4b site. For (Pr1-xYx)3RuO7, with increasing the concentration of Y ions (x value), the smaller Y ions occupy selectively the seven-coordinate 8g site rather than the eight-coordinate 4a site.Through magnetic susceptibility measurements for Pr3(Ru1-xTax)O7, the antiferromagnetic transition temperatures decrease linearly with increasing x value, and at x=0.75 no magnetic ordering was found down to 1.8K, indicating the magnetic interaction is not one-dimensional, but three-dimensional. On the other hand, the antiferromagnetic transition temperature for (Pr1-xYx)3RuO7 decreases with increasing x value, but above x≥0.50 it becomes constant (~12K). This result indicates that Pr3+ ions at the seven-coordinate site greatly contribute to the antiferromagnetic interactions observed in (Pr1-xYx)3RuO7.Density functional calculations of Pr3RuO7 demonstrate that the electronic structure gives insulating character and that oxygen 2p orbitals hybridize strongly with Ru 4d orbitals in the valence band (VB). Near the top of VB, the Pr 4f orbitals at the seven-coordinated site also show a weak hybridization with the O(1) 2p orbitals. The Ru-O(1)-Pr superexchange pathway take part in three-dimensional magnetic interaction and play an important role in an enhancement of long-range magnetic ordering.

Origin of Ferromagnetism in Ru and N Codoped TiO2 Nanotubes: Experiments and Theory Investigations

The room temperature ferromagnetism (RTFM) of the undoped, N doped, Ru doped ,and Ru-N codoped anatase TiO2 nanotubes (TNTs) films are investigated combined with experiments and first principles approaches. The experiments are highly consistent with the theory calculations. All samples display anatase structures and ferromagnetism at room temperature. The values of the saturation magnetization (Ms) of undoped TiO2, N doped TiO2, Ru doped TiO2, and Ru-N codoped TiO2, respectively, are 0.065 emu/g, 0.015 emu/g, 0.155 emu/g, and 0.073 emu/g. The calculated net moment is in the order of Ru doped > Ru-N codoped > undoped > N doped. The oxygen vacancies play an important role in RTFM of TNTs. Moreover, the hybridization of Ru 4d, N 2p, and O 2p led to the spin-spilt of Ru 4d, N 2p, and O 2p which is devoted to the system magnetism.

Production of conjugated linoleic acid-rich cottonseed oil by supported Ru catalyzed isomerization

Supported metal (e.g. Ruthenium (Ru)) is capable to catalyze the isomerization of polyunsaturated fatty acids in plant oils into conjugated fatty acids. Conjugated linoleic acids (CLAs) produced from plant oils have not only been associated with diverse health and physiological effects, but also been interesting renewable compounds in producing industrial products such as paints, glues, and polymers, due to the presence of very reactive conjugated double bonds. To explore the industrial potential of heterogeneous supported metal catalyst in converting food-use limited cottonseed oil (CSO) into conjugated linoleic acid (CLA)-rich plant oil, Ru/C (J.M.), Ru/C (Sigma), Ru/Al2O3 and Ru black are examined for their catalytic efficiency/selectivity in decane and solvent-free systems. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) are employed for their surface chemical composition and morphology analyses. Deconvolution of Ru 3p and 3d spectra are executed by Gaussian and Lorentzian fitting; and a qualitative correlation between oxidation states of Ru and catalytic activity/selectivity of Ru catalysts are delineated. In 24h in solvent-free system Ru black is capable to achieve 51.3% conversion of linoleic acid (LA) in CSO with excellent selectivity (83.7%) towards CLA formation (CLA-rich CSO can be easily obtained by simple filtration); conversion of LA doesnot show any Sn-2/Sn-1,3 region-preference; however, the reaction activity/selectivity is pronouncedly correlated to the content of Ru (IV) in catalysts.

Correlation effect in Sr1−xLaxRuO3 studied by soft x-ray photoemission spectroscopy

To clarify how the electronic state of Sr1-xLaxRuO3 evolves with La doping, we conducted photoemission (PES) experiments using soft x-rays. The spectral shape of the Ru 4d derived peak near the Fermi level changes significantly with increasing x. This variation indicates that a spectral weight transfer from the coherent to incoherent component occurs due to an enhancement of the electron correlation effect. Resonant PES experiments at the La 3d_{5/2} edge have confirmed that there is no significant contribution of the La 5d state in the energy range where the spectral weight transfer is observed. Using the dependence of the photoelectron mean free path on the photon energy, we subtracted the surface components from the PES spectra and confirmed that the enhancement of the electron correlation effect with La doping is an intrinsic bulk phenomenon. On the other hand, a large portion of the coherent component remains at the Fermi level up to x = 0.5, reflecting that the Ru 4d state still has itinerant characteristics. Moreover, we found that the PES spectra hardly depend on the temperature and do not exhibit a discernible change with magnetic ordering, suggesting that the temperature variation of the exchange splitting does not follow the prediction of the Stoner theory. The presently obtained experimental results indicate that the electron correlation effect plays an important role in Sr1-xLaxRuO3 and that the Ru 4d electrons possess both local and itinerant characteristics.

Enhanced metallic properties of SrRuO3 thin films via kinetically controlled pulsed laser epitaxy

Metal electrodes are a universal element of all electronic devices. Conducting SrRuO3 (SRO) epitaxial thin films have been extensively used as electrodes in complex-oxide heterostructures due to good lattice mismatches with perovskite substrates. However, when compared to SRO single crystals, SRO thin films have shown reduced conductivity and Curie temperatures (TC), which can lead to higher Joule heating and energy loss in the devices. Here, we report that high-quality SRO thin films can be synthesized by controlling the plume dynamics and growth rate of pulsed laser epitaxy (PLE) with real-time optical spectroscopic monitoring. The SRO thin films grown under the kinetically controlled conditions, down to ca. 16 nm in thickness, exhibit both enhanced conductivity and TC as compared to bulk values, due to their improved stoichiometry and a strain-mediated increase of the bandwidth of Ru 4d electrons. This result provides a direction for enhancing the physical properties of PLE-grown thin films and paves a way to improved device applications.

Epitaxial synthesis and physical properties of double-perovskite oxide Sr2CoRuO6 thin films

We report epitaxial structures and physical properties of double-perovskite Sr2CoRuO6 films grown using pulsed-laser deposition. Samples with a degree of Co/Ru order of 2–73% were obtained by changing growth temperature. X-ray absorption spectroscopy (XAS) on the highest ordered sample revealed that Co ions were trivalent with a high-spin configuration and Ru ions were pentavalent. We found large differences in magnetization and resistivity between the highest and lowest ordered samples as well as the absence of strong magnetism and metallicity, which are common characteristics of SrCoO3 and SrRuO3. Using resonant photoemission spectroscopy and XAS, dominant d-orbital components at the top of the occupied state (the bottom of the unoccupied state) were identified to be Ru 4d t2g (Co 3d and Ru 4d t2g). These results suggest that the ground state of double-perovskite Sr2CoRuO6 is a ferrimagnetic insulator.

Insight into the magnetism of a distorted Kagome lattice, Dy3Ru4Al12, based on polycrystalline studies

The layered compound with distorted Kagome nets, Dy3Ru4Al12, was previously reported to undergo antiferromagnetic ordering below (TN=) 7 K, based on investigations on single crystals. Here, we report the results of our investigation of AC and DC magnetic susceptibility (χ), isothermal remnant magnetization (MIRM), heat-capacity, magnetocaloric effect and magnetoresistance measurements on polycrystals. The present results reveal that there is an additional magnetic anomaly around 20 K, as though the Néel order is preceded by the formation of ferromagnetic clusters. We attribute this feature to geometric frustration of magnetism. In view of the existence of this phase, the interpretation of the linear-term in the heat-capacity in terms of spin-fluctuations from the Ru 4d band needs to be revisited. Additionally, in the vicinity of TN, AC χ shows a prominent frequency dependence and, below TN, MIRM exhibits a slow decay with time. This raises a question whether the antiferromagnetic structure in this compound is characterized by spin-glass-like dynamics. In contrast to what was reported earlier, there is a change in the sign of the magnetoresistance (MR) at the metamagnetic transition. A butter-fly-shaped (isothermal) MR loop (interestingly spanning over all the four quadrants) is observed at 2 K with distinct evidence for the magnetic phase co-existence phenomenon in zero field after travelling through metamagnetic transition field. The results on polycrystals thus provide additional information about the magnetism of this compound, revealing that the magnetism of this compound is more complex than what is believed, due to geometric frustration intrinsic to Kagome net.

Operando Soft X-Ray Absorption Study on Electronic Structure of Lithium-Rich Cathode Materials; Li2MnO3 and Li2RuO3

High capacity cathode materials of lithium ion secondary battery are desirable to apply to the large-scaled energy devices such as electric vehicles or electricity storage systems. Recently, lithium-rich layered materials such as Li2MnO3 and Li2RuO3 are attended as interesting cathode materials because of their a few times larger theoretical capacity than that of LiCoO2 [1].The reaction mechanism of the lithium-rich cathodes has not been fully understood, especially at the high potential. In this study, Li2MnO3 and Li2RuO3 electrodes were prepared, and the electronic structure change of Li2MnO3 and Li2RuO3 were investigated by using operandosoft X-ray absorption spectroscopy under charge-discharge reaction of these electrodes. The cathode materials were synthesized by solid-state reaction method. Li2MnO3 was prepared from a stoichiometric amount of LiOH-H2O and MnO2. They were dispersed in acetone and ground by a ball milling machine for 3 hours at a speed of 400 rpm using 2 mm ZrO2 beads as grinding media. After drying, the mixture powder was pressed into pellets (10 mm diameter.) and heated at 450 °C for 24 hours in air and then calcined at 400 °C for 48 hours. Li2RuO3 was prepared from LiOH-H2O and RuO2in the same way, however, heated at 1000 °C for 15 hours in air and then ground for 3 hours before calcined at 900 °C for an hour. The cathode for operando X-ray absorption measurements was prepared from a paste by mixing 80 wt% of as-prepared cathode active materials, 10 wt% of acetylene black and 10 wt% of polyvinylidene difluoride binder in 1-methyl-2-pyrrolidone solvent. This paste was coated on the platinum-sputtered silicon nitride thin film. Li4Ti5O12 was used as the counter electrode material and 1 mol/L LiPF6 in an acetonitrile solvent was used as an electrolyte. The operando soft X-ray absorption spectroscopy measurement was carried out at BL27SU of SPring-8. The oxygen K-edge XANES spectra for Li2MnO3 and Li2RuO3 during first charge reaction were measured. For the charge reaction of Li2MnO3, the peaks located at 529.5 eV and 532.0 eV were progressively weaken and broadened (Figure 1a). It implies that the main reaction during the charge process is the oxygen evolution because of the small contribution of Mn 3d - O 2p orbital. For Li2RuO3 (Figure 1b), on the other hand, the peaks at 529.5 eV and 532.0 eV were shifted to the lower energy during the delithiated process from x=2.00 to x=1.00 in LixRuO3 and these peaks were sharpen from x=1.00 to x=0.48. In the Ru L3-egde XANES spectra, the peak was shifted to the higher energy from x=2.00 to x=1.00, however not changed from x=1.00 to x=0.48. These results suggest that the Li2RuO3 charge reaction includes two process, (1) the oxidized reaction of Ru4+→Ru5+, (2) O2 charge compensation owing to the hybridization state between Ru 4d and O 2porbital. This work revealed the contribution of the Ru-O hybrid orbital during the charge process directly and was a guide to design the high-capacity cathode materials in the future. Reference [1] M. Sathiya, K. Ramesha, G. Rousse, D. Foix, D. Gonbeau, A. S. Prakash, M. L. Doublet, K. Hemalatha, and J.-M. Tarascon, Chem. Mater. 25(2013), 1121−1131

Copper oxide surfaces modified by alkylphosphonic acids with terminal pyridyl-based ligands as a platform for supported catalysis

Self-assembled monolayer (SAM) films of phosphonates have been successfully formed via reaction of 11-hydroxyundecylphosphonic acid or 4,4′-di(methylenephosphonic acid)-2,2′-bipyridine with the oxide layer of copper via the Tethering by Aggregation and Growth (TBAG) deposition method. The hydroxyl-terminated SAM was further modified with isonicotinic acid or 4,4′-dicarboxy-2,2′-bipyridine through a Steglich esterification reaction. These three surfaces derivatized with pyridyl-based ligands are potential platforms for supported catalysis. As a proof of concept, [Ru(CO)3Cl2]2 was bound to the surfaces through the pyridyl-based ligands to yield tethered analogs of the known carbon dioxide reduction catalyst, [Ru(bpy)(CO)2Cl2]. Surface modification reactions were confirmed through specular reflectance infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Characteristic core binding energies were observed in the XPS analyses for phosphorus (P 2p), nitrogen (N 1s), and ruthenium (Ru 3p and Ru 3d), verifying the presence of the various surface functionalizations. IR and XPS data indicate that the phosphonate binding to the copper surface is tridentate in nature.

Near Ambient Pressure X-ray Photoelectron Spectroscopy Study of the Atomic Layer Deposition of TiO2 on RuO2(110)

The atomic layer deposition (ALD) of TiO2 on a RuO2(110) surface from tetrakis(dimethylamido) titanium and water at 110 °C was investigated using near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) at precursor pressures up to 0.1 mbar. In addition to the expected cyclic surface species, evidence for side reactions was found. Dimethylamine adsorbs on the surface during the TDMAT half-cycle, and a second species, likely methyl methylenimine, also forms. The removal of the amide ligand and the formation of an alkyammonium species during the water half-cycle were found to be pressure dependent. The O 1s, Ru 3d, and Ti 2p spectra show the formation of the Ru–O–Ti interface, and the binding energies are consistent with formation of TiO2 after one full ALD cycle. Dosing TDMAT on the RuO2(110) surface at room temperature promotes a multilayer formation that begins to desorb at 40 °C. The imine species is not seen until 60 °C. These insights into the ALD mechanism and precursor pressure dependence on...

Resolving ruthenium: XPS studies of common ruthenium materials

X‐ray photoelectron spectroscopy (XPS) utilising monochromatic Al Kα radiation has been employed to study metallic ruthenium and the catalytically and technologically important ruthenium compounds RuO2, RuCl3, Ru(NO)(NO3)3 and Ru(AcAc)3. The results improve on the accuracy of already published Ru(3d) binding energies, expand known Ru(3p) binding energies and also report spin‐orbit splitting for the core levels. For RuO2, the difference between anhydrous and hydrated samples is explored, and the effect on curve fitting such spectra is discussed. Analysis of RuCl3 has allowed, for the first time, the positive identification of Ru(OH)3 by XPS. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of the Ir Impurity on the Thermodynamic and Transport Properties of Ba4Ru3O10

We report the effects of Ir impurity on the physical properties of Ba4Ru3−xIrxO10 (0 ≤ x ≤ 0.5) which is composed of three face-shared RuO6 octahedra (Ru trimer). We discuss the origin of the unique electronic phase transition from paramagnetic metal to antiferromagnetic insulator at 105 K in terms of hybridized orbitals of Ru 4d in the Ru trimer. From the magnetic susceptibility and the specific heat, the transition temperature is found to decrease more remarkably than is expected in typical diluted magnets and is hardly discernible at around x = 0.5, while the magnetic interaction only decreases slightly with x. This implies that the transition is not driven by magnetic interaction. In contrast, the hump due to the phase transition still remains in the Seebeck coefficient for x = 0.5, which means that the charge gap still remains as a short-range order. Since the charge gap originates from the 4d hybridization in the Ru trimer, intra-trimer charge transfer is likely to dominate the transition.

Effective mass enhancement in B site Fe doping heavy fermion compound CaCu3Ru4O12

Abstract Polycrystalline samples of CaCu 3 Ru 4− x Fe x O 12 ( x =0, 0.04, 0.1, 0.2) were synthesized via conventional solid state reactions. The specific heats of these four compounds have been investigated at temperature down to 2 K. Following the Fe doping, the linear electronic specific heat coefficient increased from 90 mJ/(f.u. mol K 2 ) for x =0 to 271 mJ/(f.u. mol) for x =0.2, indicating an effective mass enhancement. We propose that such enhancement mainly comes from the additional Kondo coupling between the itinerant electrons in Ru 4d orbitals and the localized electrons in 3d orbitals of Fe dopants. Moreover, below a certain temperature, an upturn appears in the C p / T – T 2 curves for all the Fe doped samples CaCu 3 Ru 4− x Fe x O 12 with x ≤0.2. The origin of this upturn may be a new magnetic order state which needs to be identified with further investigations.

Carbon–Hydrogen Bond Activation in Bis(2,6-dimethylbenzenethiolato)tris(trimethylphosphine)ruthenium(II): Ligand Dances and Solvent Transformations

Density functional theory (DFT) calculations are used to predict the mechanism for the intramolecular carbon–hydrogen bond activation of an ortho methyl group on the RuII(SC6H3Me2-2,6-κ1S)2(PMe3)3 complex to form the cycloruthenated product cis-Ru[SC6H3-(2-CH2)(6-Me)-κ2S2C](PMe3)4 and HSC6H3Me2-2,6 in the presence of PMe3. The DFT calculations also show how changing the solvent from benzene to methanol prevents C–H activation and results in the unactivated six-coordinate product Ru(SC6H3Me2-2,6-κ1S)2(PMe3)4 in 100% yield. The reactant was determined to have two plausible σ-bond metathesis pathways in which to react, one for each of the two thiolate ligands. The steps in both mechanisms were influenced by the electronic interactions between the sulfur lone pairs and the Ru 4d orbitals and the steric repulsion between the methyl groups on the five ligands in such a way that the methyl group in the SAr (Ar = SC6H3Me2-2,6) ligand closest to the Ru pirouettes away to activate the other methyl group. The equato...

Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer.

Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse.

Soft landing of bare PtRu nanoparticles for electrochemical reduction of oxygen.

Magnetron sputtering of two independent Pt and Ru targets coupled with inert gas aggregation in a modified commercial source has been combined with soft landing of mass-selected ions to prepare bare 4.5 nm diameter PtRu nanoparticles on glassy carbon electrodes with controlled size and morphology for electrochemical reduction of oxygen in solution. Employing atomic force microscopy (AFM) it is shown that the nanoparticles bind randomly to the glassy carbon electrode at a relatively low coverage of 7 × 10(4) ions μm(-2) and that their average height is centered at 4.5 nm. Scanning transmission electron microscopy images obtained in the high-angle annular dark field mode (HAADF-STEM) further confirm that the soft-landed PtRu nanoparticles are uniform in size. Wide-area scans of the electrodes using X-ray photoelectron spectroscopy (XPS) reveal the presence of both Pt and Ru in atomic concentrations of ∼9% and ∼33%, respectively. Deconvolution of the high energy resolution XPS spectra in the Pt 4f and Ru 3d regions indicates the presence of both oxidized Pt and Ru. The substantially higher loading of Ru compared to Pt and enrichment of Pt at the surface of the nanoparticles is confirmed by wide-area analysis of the electrodes using time-of-flight medium energy ion scattering (TOF-MEIS) employing both 80 keV He(+) and O(+) ions. The activity of electrodes containing 7 × 10(4) ions μm(-2) of bare 4.5 nm PtRu nanoparticles toward the electrochemical reduction of oxygen was evaluated employing cyclic voltammetry (CV) in 0.1 M HClO4 and 0.5 M H2SO4 solutions. In both electrolytes a pronounced reduction peak was observed during O2 purging of the solution that was not evident during purging with Ar. Repeated electrochemical cycling of the electrodes revealed little evolution in the shape or position of the voltammograms indicating high stability of the nanoparticles supported on glassy carbon. The reproducibility of the nanoparticle synthesis and deposition was evaluated by employing the same experimental parameters to prepare nanoparticles on glassy carbon electrodes on three occasions separated by several days. Surfaces with almost identical electrochemical behavior were observed with CV, demonstrating the highly reproducible preparation of bare nanoparticles using physical synthesis in the gas-phase combined with soft landing of mass-selected ions.