Ion Scattering Spectroscopy Research Articles

Resonant Charge-Transfer in Grazing Collisions of H− with Vicinal Nanosurfaces on Cu(111), Au(100) and Pd(111) Substrates: A Comparative Study

We compare the electron dynamics at monocrystalline Cu(111), Au(100) and Pd(111) precursor substrates with vicinal nanosteps. The unoccupied bands of a surface superlattice are populated via the resonant charge transfer (RCT) between the surface and a H − ion that flies by at grazing angles. A quantum mechanical wave packet propagation approach is used to simulate the motion of the active electron, and time-evolved wave packet densities are used to visualize the dynamics through the superlattice. The survived ion fraction in the reflected beam generally exhibits modulations as a function of the vicinal terrace size and shows peaks at those energies that access the image state subband dispersions. Differences in magnitudes of the ion-survival as a function of the particular substrate selection and the ion-surface interaction time, based on the choice of two ion-trajectories, are examined. A square well model, producing standing waves between the steps on the surface, explains the energies of the maxima in the ion survival probability for all the metals considered. This indicates that the primary process of confinement induced subband formation is robust. The work may motivate measurements and applications of shallow-angle ion-scattering spectroscopy to access electronic substructures in periodically nanostructured surfaces.

Oxygen Reduction Reaction Activity for Surface-Magnetic-Anisotropy-Controlled Pt-Co/Pt(111) Bimetallic Surface

Introduction Developments in effective oxygen reduction reaction (ORR) catalysts for the cathode of Polymer Electrolyte Fuel Cell is important to achieve “hydrogen society”. Because oxygen molecules (O2), the reactant of ORR, is paramagnetic having a triplet spin state, ORR that proceeds on the cathode catalyst surfaces might modify by magnetism of the catalyst materials. Indeed, ORR activity was improved by the influence of an external magnetic field applied to the catalyst [1]. The alloys of 3d transition magnetic elements M (M=Co, Fe, Ni) are known to exhibit ferromagnetism. Etz et al. reported that the direction of magnetization easy axis of the epitaxial Co/Pt(111) surface depends on the Co deposition thickness [2]. However, to our best knowledge, relation between the magnetic anisotropy of the cathode electrode surface and ORR activity is yet to be clarified. Therefore, to investigate influence of spontaneous magnetization of the material’s surface on the ORR should cast some light on the ORR activity enhancement mechanisms for such the Pt-M alloy surfaces with the magnetic. In this study, we fabricate Pt-Co/Pt(111) ferromagnetic bimetallic surfaces under ultra-high vacuum (UHV) through 1 monolayer(ML)-thick epitaxial growth of Co on the clean Pt(111) substrate at various temperatures and discuss the influence of magnetic anisotropy of the Pt-Co/Pt(111) bimetallic surface on corresponding ORR activity. Experimental The sample fabrication process of Pt-Co/Pt(111) bimetallic surface is as follows. After surface cleaning of the Pt(111) single crystal substrate through Ar+ sputtering and annealing at 1173 K in ultra-high vacuum (UHV: 10-8 Pa), 1ML-thick-Co was deposited on the clean Pt(111) by the molecular-beam epitaxy (MBE) method at elevated substrate temperature (723 K to 973 K) to generate the Pt(111)-skin through the surface segregation of substrate Pt atoms [3]. The Pt-Co/Pt(111) bimetallic surfaces are described hereafter by the Co deposition temperatures, for example Pt-Co773K/Pt(111), etc. The resulting surface structures were verified by the scanning tunneling microscopy (STM) and low-energy ion scattering spectroscopy (LE-ISS) in UHV. Then, polar magneto optical Kerr effect (polar MOKE), and in-plane XRD measurements are conducted in air to evaluate the surface magnetic anisotropies and compressive strains of the generated Pt(111)-skin surfaces. The MBE-prepared samples were transferred to electrochemical evaluation systems set in a N2–purged glove box without being exposed to air. Then, cyclic voltammetry (CV) and linear sweep voltammetry (LSV) measurements were conducted in N2–purged and O2–saturated 0.1 M HClO4, respectively, in the glove box. ORR activities of the samples were evaluated based on j k values at 0.9 V vs. RHE by using Koutecky–Levich equation. Results and Discussion An LE-ISS spectrum of the Pt-Co773K/Pt(111) is shown in Fig. 1(a). Only the signal due to of the Pt atoms at the topmost surface is appeared on the spectrum, indicating that the Pt(111)-skin is generated for the Pt-Co773K/Pt(111) surface and the deposited Co should be located below the second atomic layer of the Pt-Co773K/Pt(111) as a result of surface segregation of the substrate Pt atoms at deposition temperature (of 773 K). Fig. 1(b) shows an STM image of the corresponding Pt-Co773K/Pt(111) surface. As shown in Fig. 1(b), the sample surface is atomically flat. One might notice that Moiré-pattern-like surface corrugations on the image (highlighted by white line), probably stemming from the lattice mismatch between Pt(111)-skin and underlying Co (Pt-Co alloy) [4]. The result also supports the Pt(111)-skin. Fig. 1(c) shows the polar MOKE curves of the Pt-Co773K/Pt(111) (red) and Pt-Co823K/Pt(111) (blue). Both the samples show the hysteresis loops of Kerr rotation angle vs. magnetic field H, indicating that perpendicular magnetic anisotropy (PMA) of the sample surfaces. Relation between the ORR activities and in-plane-XRD-estimated compressive strains of the Pt-Co773K/Pt(111) (red) and Pt-Co873K/Pt(111) (blue) surfaces are shown in Fig. 1(d). For comparison, the DFT-calculated ORR activities of the strained Pt(111) surfaces (green) are plotted in the figure [5]. The estimated ORR activities for both the Pt-Co773K/Pt(111) and Pt-Co873K/Pt(111) are 20 to 30 % higher than the DFT-calculated ones. The results suggest that PMA might affect ORR activity enhancements for the prepared PMA surfaces of the Pt-Co/Pt(111). At the meeting, effects of magnetic anisotropies (perpendicular and in-plane) are discussed more in detail.

Electrochemical Preparation of TiOx-Electrodes: Effect of the Counter Electrode on the Charge Transfer Properties

Sub-stoichiometric titanium dioxide (TiOx) is known for its corrosion resistance and electrical conductivity.1 Thus, it is recognized as promising material for (photo-)electrochemical applications and used as protective layer in PEC water splitting or electrode material for water treatment.1,2 In general, its properties strongly depend on the synthesis and the conductivity of TiOx can be tuned by its Ti/O ratio.1,3 TiOx is commonly prepared by hydrogenation;3 however, the requirements for high pressure, high temperature and hydrogen atmosphere are cumbersome imposing a potential safety risk. Over the past years, electrochemical preparation of TiOx via cathodic polarization of TiO2 substrates became an interesting alternative.4 Pt is widely used in electrochemistry as counter electrode5 and frequently applied for TiOx preparation;4 however, the suitability of Pt as (anodic) counter electrode (CE) is questionable since the stability of Pt is often overestimated.5 As Pt contamination can severely influence the electrocatalytic properties this study focuses on the preparation of TiOx using three different CE (Pt, Iridium mixed metal oxide, Boron doped diamond) and the influence of the CE will be discussed in detail. It will be shown using state of the art techniques such as SEM, XPS and highly surface sensitive low energy ion scattering (LEIS) spectroscopy that indeed Pt contamination dominates the properties of TiOx (Figure 1a). In contrast, for Iridium mixed metal oxide and Boron doped diamond CEs no related contaminations were observed allowing to determine the intrinsic properties of TiOx electrodes. Using Fe2 +/3+ redox couple experiments and electrochemical impedance spectroscopy we determined the charge transfer properties of the TiOx electrodes prepared with BDD and IrMMO (Figure 1b). Although both BDD and IrMMO appear to be suited for the preparation of TiOx differences in the doping are observed that will be discussed in detail in this contribution.

The influence of surface defects on the low energy scattering of Ar ions from a Cu(111) surface

Low-energy ion scattering (LEIS) is distinguished by its acute surface sensitivity. Depending on the projectile/target system under analysis and the incoming energy of the projectile, it can provide information on the outermost atomic layer of the target surface. Due to the range of energies involved in LEIS, an elemental model based on a two-body classical elastic collision is generally accepted to describe the energy-position of all the peaks appearing in a LEIS spectrum. Here, we show that, under specific experimental conditions for Ar+ ions colliding with a Cu(111) surface, there exist certain peaks in the LEIS spectra that cannot be explained by the binary collision model. We experimentally show also that the appearance of these peaks is strongly dependent on the experimental conditions. We use molecular dynamics simulations to describe and understand the physical processes behind these particular features in the LEIS spectrum. We determine that surface defects such as islands or steps, inherent to any real physical surface, are crucial to the existence of the mentioned singular features in the Ar/Cu LEIS spectrum.

Growth and Oxidation of Zinc on Cu(111)

Zinc and zinc oxide films on Cu(111) have frequently been used as inverse model catalysts to study various chemical reactions. In the present work the growth and subsequent oxidation of zinc films are investigated by scanning tunneling microscopy (STM), low-energy ion scattering (LEIS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED). Up to monolayer coverage zinc grows as a two-dimensional film with zinc atoms continuing the face-centered cubic lattice of the copper substrate. At higher coverages layer-by-layer growth is less strictly obeyed. Stacking faults are introduced as well, indicating a transition toward a hexagonal-close-packed structure of zinc. At 300 K intermixing is found to be slow but rises when the temperature is increased. Accordingly, the continuous downshift and broadening of the zinc desorption peak with increasing submonolayer coverage are attributed to different levels of intermixing formed during the TPD temperature ramp. Postoxidation of zinc fi...

Growth of ultrathin Ru oxide films on perovskite and corundum substrates

The ability to control the dispersion of RuO2 monolayers on a range of perovskite- and corundum-structured oxide substrates was investigated using complementary experiment and theory. Controlled deposition under UHV conditions and subsequent in situ characterization by x-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), reflection high energy electron diffraction (RHEED) and low energy electron diffraction (LEED) was used to follow the chemical state, dispersion and structure of the RuO2 layers as a function of growth and post-growth processing conditions. The experimental results reveal that monolayer RuO2 on ferroelectric PbxZr1-xTiO3(001) and non-polar SrTiO3(001) α-Al2O3(11¯02) tends to dewet the surface to form three-dimensional clusters, though some kinetic stability of dispersed RuO2 monolayers was achieved on the SrTiO3 surface. Although an RuO2 termination is not favored for SrRuO3(001), deposition onto SrRuO3(001) yields a stable RuO2 surface which ISS suggests is capped by chemisorbed oxygen. The complementary density functional theory modeling and ab initio thermodynamics indicate that Ru oxide monolayers on the perovskite substrates tend to be unstable under the low oxygen pressure experimental conditions; however, either lower temperatures or higher oxygen pressures can lead to a kinetic and even thermodynamic stability. The theoretical findings also provide guidance on how the instability of dispersed RuO2 monolayers can be overcome by inserting buffer layers and increasing the partial pressure of molecules that selectively, strongly adsorb at coordinatively unsaturated Ru sites on the oxide surface.

(Invited) Enhancing SOFC Anode Stability through Atomic Layer Deposition

Ni-YSZ cermet anodes are highly optimized to achieve good mechanical strength and electrochemical performance. However, they still suffer from sensitivity to impurities like sulfur, poor redox stability, and a tendency to form carbon fibers if the H2O:C ratio is too low or there are higher hydrocarbons in the feed to the cell. In this project we utilize atomic layer deposition (ALD) to grow thin oxide films onto the anode surface to enhance both the thermal stability and coking tolerance of the Ni-YSZ cermet. We have developed an ALD system that enables controlled, sub-monolayer conformal coating of mixed metal oxide films. The growth process, coverage, composition and operational stability of these films is carefully analyzed utilizing a unique High-Sensitivity Low Energy Ion Scattering (HS-LEIS) instrument that provides the composition of the outermost atomic surface layer of the material. This ex-situ characterization is closely correlated to the electrochemical performance of the anodes.

Synthesis and Growth Mechanism of Stable Prenucleated (≈0.8 nm Diameter) PbS Quantum Dots by Medium Energy Ion Scattering Spectroscopy.

In the current work, stable prenucleated PbS quantum dots (QDs) with a sub-nanometer (0.8 nm) size have been successfully synthesized via a systematically designed experiment. A detailed analysis of critical nucleation, growth, and stability for such ultrasmall prenucleated clusters is done. The experimental strategy is based on controlled concentration, temperature and injection of respective precursors, thus enabling us to control nucleation rate and separation of stable sub-nanometer PbS QDs with size 0.8 nm. Significantly, by providing additional thermal energy to sub-nanometer PbS QDs, we achieved the fully nucleated cubic crystalline structure of PbS with size of around 1.5 nm. The size and composition of the prenucleated QDs are investigated by sophisticated tools like X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS) spectroscopy which confirms the synthesis of PbS with Pb2+ rich surface while the UV-Vis spectroscopy and X-ray diffraction (XRD) data suggests an alternative crystallization path. Non-classical nucleation theory is employed to substantiate the growth mechanism of prenucleated PbS QDs.

Impact of Surface Composition of SrTiO3 Catalysts for Oxidative Coupling of Methane

AbstractOxidative coupling of methane (OCM) to C2 hydrocarbons (C2H6 and C2H4) have regained much attention due to the shale gas revolution. Perovskite catalysts have shown promising activity and selectivity to C2 hydrocarbons. Here, we investigate the effect of surface reconstruction (leading to different surface compositions) of perovskites on the OCM by using SrTiO3(STO) as a model catalyst. Different surface densities of Sr (25–96 %) were attained via various treatments of STO. Low energy ion scattering (LEIS) and UV‐Raman results are in good agreement on the surface and subsurface composition of the reconstructed STO. From H2‐TPR, the same H2 consumption of STO samples allows relating their catalytic performances with surface acid‐base properties (quantified by NH3‐/CO2‐TPD). At 600–800 °C, the surface Sr enrichment was found to enhance CH4 conversion, C2 selectivity and the ratio C2H4/C2H6 up to Sr/(Sr+Ti) of 0.66 and then levels off. Furthermore, the relative concentration of basic sites, base/(base+acid), is found as a better descriptor for STO catalytic performances. This work shows the clear correlation between surface reconstruction, relative basicity/acidity and OCM catalytic performance over perovskite catalysts. The trends here are similar to those for CH4 combustion over the reconstructed STO in our recent work. Overall, we suggest that tuning surface reconstruction/composition of perovskites can be an effective approach to control CH4 activation and conversions.

Thermal properties and segregation phenomena in transition metals and alloys: modeling based on modified cohesive-energies

In spite of free-atom electronic-relaxation contributions to transition-metal cohesive-energies, numerous studies have misused the latter instead of using the solid-state interatomic bond-energy in modeling bulk and surface properties. This work reveals that eliminating the free-atom contributions from experimental cohesive-energies leads to highly accurate linear correlations of the resultant bond-energies with melting temperatures and enthalpies, as well as with inverse thermal-expansion coefficients, specifically for the fcc transition-metals. Likewise, predictions of surface segregation phenomena in Cu–Pd and Au–Pd alloys on the basis of the modified energetics are in much better agreement with reported low-energy ion scattering spectroscopy (LEISS) experimental results, as compared to the use of cohesive-energy values. A last demonstration of the problem and its solution involves the significant impact of the modification on segregation (separation) phase transitions in Cu–Ni model nanoparticles.

Surface composition of ion bombarded nickel based alloys

The composition of NixPdy (x, y = 1, 5) and NiMoRe alloys irradiated by 3 and 4 keV Ar+ ions along the normal to the sample surface was investigated in situ by low energy ion scattering spectroscopy (LEIS). The analysis was performed using a 5 keV Ne+ ion beam. It was found that the composition of the topmost layer of bombarded NixPdy alloys nearly corresponds to the alloy stoichiometry. In the case of irradiation of the NiMoRe alloy, a surface enrichment with the heavier components (Mo and Re) was found. The thermally activated Gibbsian segregation in NiPd and NiPd5 alloys was also studied using LEIS.

Surface Compositions of Oxide Supported Bimetallic Catalysts: A Compared Study by High-Sensitivity Low Energy Ion Scattering Spectroscopy and X-Ray Photoemission Spectroscopy.

It is well known that there is a critical relationship between the surface composition and catalytic performance for a bimetallic catalyst. However, in most cases, the surface composition is obviously different from that of the bulk. Moreover, the surface is normally reconstructed under reaction conditions. In this personal account, our recent progresses in determining the surface compositions of oxide supported bimetal catalysts by high-sensitivity low energy ion scattering spectroscopy (HS-LEIS) and X-ray photoemission spectroscopy (XPS) are summarized. Phase diagrams of the surface compositions under various conditions as a function of the bulk composition are established and compared. It is found that oxidation induces de-alloying and enrichment of PdO, CuO, SnO2 on the surface, while H2 reduction results in re-alloying. The addition of the second component not only modifies the nature of the active site, but also varies the dispersion of the active components. The support effects are discussed. The compared studies reveal that HS-LEIS can achieve a more reliable surface composition for oxide supported catalysts.

Perovskite oxides for redox oxidative cracking of n-hexane under a cyclic redox scheme

Steam cracking of naphtha is a commercially proven technology for light olefin production and the primary source of ethylene in the Europe and Asia-Pacific markets. However, its significant energy consumption and high CO2 intensity (up to 2 tons CO2/ton C2H4), stemming from endothermic cracking reactions and complex product separations, make this state-of-the-art process increasingly undesirable from an environmental standpoint. We propose a redox oxidative cracking (ROC) approach as an alternative pathway for naphtha conversion. Enabled by perovskite oxide-based redox catalysts, the ROC process converts naphtha (represented by n-hexane) in an auto-thermal, cyclic redox mode. The addition of 20 wt.% Na2WO4 to SrMnO3 and CaMnO3 created highly selective redox catalysts capable of achieving enhanced olefin yields from n-hexane oxy-cracking. This was largely attributed to the redox catalysts’ high activity, selectivity, and stability towards selective hydrogen combustion (SHC) under a redox mode. Na2WO4/CaMnO3 demonstrated significantly higher olefin yield (55–58%) when compared to that from thermal cracking (34%) at 725 °C and 4500 h−1. COx yield as low as 1.7% was achieved along with complete combustion of H2 over 25 cycles. Similarly, Na2WO4/SrMnO3 achieved 41% olefin yield, 0.4% COx yield, and 73% H2 combustion at this condition. Oxygen-temperature-programmed desorption (O2-TPD) indicated that Na2WO4 hindered gaseous oxygen release from CaMnO3. Low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS) revealed an outermost perovskite surface layer covered by Na2WO4, which suppressed near-surface Mn and alkaline earth metal cations. The formation of non-selective surface oxygen species was also inhibited. XPS analysis further confirmed that promotion of SrMnO3 with Na2WO4 suppressed surface Sr species by 90%, with a similar effect also observed on CaMnO3. These findings point to the promoting effect of Na2WO4 and the potential of promoted SrMnO3 and CaMnO3 as selective redox catalysts for efficient production of light olefins from naphtha via the ROC process.

The impact of surface oxidation on energy spectra of keV ions scattered from transition metals

Studying the initial stages of surface oxidation is of great relevance to understand how oxygen alters the physical and chemical properties at the interface of the host material to the environment and is therefore, crucial for improvement in manifold technological applications. We investigated the influence of surface oxygen on ion spectra recorded for keV noble gas ions backscattered from metal surfaces in low energy ion scattering (LEIS). Initially pure Zn and Ta surfaces, chosen for their well-characterized properties in ion-neutralization in LEIS, have been oxidized and ion spectra for pure and oxidized surfaces have been compared. Oxygen on the surface significantly influences shape and intensity of the backscattered ion spectrum at all energies: for both metal systems, the surface scattered ion yield of the metal is drastically decreasing under oxygen presence. The observed decrease, however, cannot be explained by the reduction in the surface areal density of the metal constituents exclusively. At least for Zn an additional significant change in charge exchange behavior is necessary to explain the observations. In contrast to the generally observed decrease in the yield of ions scattered from the outermost surface, the change in shape and intensity of the reionization background are found to show opposing trends and different energy dependencies for Zn and Ta.

Initial Growth and Agglomeration during Atomic Layer Deposition of Nickel Sulfide

Atomic layer deposition (ALD) is a highly useful technique to grow thin film materials, and the initial growth of ALD is of particular importance for achieving high-quality materials and interfaces. In this work, we investigate the initial ALD growth of nickel sulfide (NiS) on a SiOx surface, from bis(N,N′-di-tert-butylacetamidinato)nickel(II) (Ni(amd)2) and H2S, by using the in situ techniques of X-ray photoelectron spectroscopy (XPS) and low-energy ion scattering (LEIS). The mechanism of the initial ALD growth is found to be rather different from that in the later steady film growth. In the initial ALD cycles, the XPS results show a drastic cyclic variation of the signals for the Ni–O bonds, with prominently observable Ni–O signals after each Ni(amd)2 dose but almost negligible after the subsequent H2S dose. These results suggest that the Ni–O bonds are first formed on the surface in the Ni(amd)2 half-cycles and then mostly converted to NiS in the following H2S half-cycles. To describe this initial ALD ...

Nano strain induced double columnar oxide as highly active oxygen-dissociation electrode for Ni-Fe metal supported solid oxide fuel cells

A double columnar structure film consisting of Sm0.5Sr0.5CoO3-δ (SSC) and Sm0.2Ce0.8O3-δ (SDC) as an active cathode was prepared by pulsed laser deposition (PLD) on a thin La0.9Sr0.1Ga0.8Mg0.2O3-δ/SDC bi-layer film, and the effects of SSC/SDC ratio in double columnar layer on cathodic performance were investigated. It was found that the cathodic overpotential as well as power density were strongly dependent on SSC-SDC ratio in double columnar layer. Almost the theoretical open circuit potential (1.10 V) and extremely high maximum power density higher than 3.0 and 0.33 W/cm2 at 973 and 773 K respectively, were achieved on the cell using double columnar at SSC:SDC= 6:4 cathode, which is the optimized composition. Increased cathodic performance of double columnar SSC-SDC cathode were assigned to the decreased activation and the concentration overpotential. From XRD and TEM analysis, tensile strain in SDC and compressed one in SSC were observed, which could be increased diffusivity of oxide ion in SDC part. On the other hand, Sr surface segregation in SSC was prevented by the double columnar structure from low energy ion scattering (LEIS) spectroscopy and this could be related to the compressed strain in SSC part of double columnar structure resulting in the increased surface activity to oxygen dissociation.

Band Structure Effects on the Charge Exchange Processes in H+ Colliding with a Cu(111) Surface

The low-energy ion scattering (LEIS) technique was used to experimentally determine the formation of positive and negative ions in the scattering of protons by a Cu(111) surface for a large scattering angle in the backscattering configuration and a wide range of incoming energies (2–8 keV). Two different collisional geometries were analyzed for a 135° fixed scattering angle: 45°/90° and 67.5°/67.5° incoming/exit angles measured with respect to the target surface. The total fraction of backscattered ions ranges from 10% to 25%, and a peculiarly high yield of negative ions, which always exceeds that of positive ions, was detected for the whole energy range analyzed. A strong dependence of the measured ion fractions with the geometrical conditions was experimentally found. On the theoretical side, a first-principles quantum-mechanical formalism that takes into account the three possible final charge states of the H+ in a correlated way and the fine details of the band structure of the Cu(111) surface was app...

Impact of nanoparticle size and lattice oxygen on water oxidation on NiFeOxHy

NiFeOxHy are the most active catalysts for oxygen evolution in a base. For this reason, they are used widely in alkaline electrolysers. Several open questions remain as to the reason for their exceptionally high catalytic activity. Here we use a model system of mass-selected NiFe nanoparticles and isotope labelling experiments to show that oxygen evolution in 1 M KOH does not proceed via lattice exchange. We complement our activity measurements with electrochemistry–mass spectrometry, taken under operando conditions, and transmission electron microscopy and low-energy ion-scattering spectroscopy, taken ex situ. Together with the trends in particle size, the isotope results indicate that oxygen evolution is limited to the near-surface region. Using the surface area of the particles, we determined that the turnover frequency was 6.2 ± 1.6 s−1 at an overpotential of 0.3 V, which is, to the best of our knowledge, the highest reported for oxygen evolution in alkaline solution. The reason for the high water-oxidation activity of Ni(Fe)OxHy catalysts in alkaline electrolyte is not yet well understood. Now, Chorkendorff and co-workers report that oxygen evolution is limited to the near-surface region by measuring the activity trends of mass-selected NiFe nanoparticles.

Cytocompatibility assessment of Ti-Nb-Zr-Si thin film metallic glasses with enhanced osteoblast differentiation for biomedical applications.

Biologically safe Ti-based quaternary Ti-Nb-Zr-Si thin film metallic glass (TFMG) was fabricated by sputtering on Titanium alloy (Ti6Al4V or Ti alloy) substrates. A preliminary assessment regarding glass forming ability, thermal stability and corrosion behavior was performed. The amorphous nature of the film is evidenced from the X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) and Selected Area Electron Diffraction (SAED) patterns. Ion scattering spectroscopy (ISS) and X-ray Photoelectron Spectroscopy (XPS) were used to analyse the chemical composition of surface which indicated oxygen on the top surface of the film and confirms the presence of Ti, Nb, Si, Zr without any other impurities. The surface morphology of the film showed a smooth surface as observed from scanning electron microscope (SEM) and atomic force microscope (AFM) analysis. It is found that the TFMG can sustain in the body-fluid, exhibiting superior corrosion resistance and electrochemical stability than the bare titanium. The cytotoxicity studies with L929 fibroblast cells showed that coatings were graded as zero and non-cytotoxic in nature. No hemolysis was observed on the coated surface indicating a better hemocompatibility. Assay using SaOS-2 bone cells showed good growth on the coated surfaces. The calcium assay showed that the SaOS-2 cells grown and differentiated on the control (Tissue Culture Polystyrene) TCPS surface had the highest mineral level. Higher alkaline phosphatase activity is obtained in SaOS-2 osteoblast cell cultures on TFMG than the control.

Au–Rh Surface Structures on Rh(111): DFT Insights into the Formation of an Ordered Surface Alloy

Surface alloying is an important technique to change chemical properties. In this study, by employing density functional theory (DFT) calculations, the atomic arrangements and energetics of an extensive set of Au–Rh structures in a confined (2 × 1) surface cell on a Rh(111) substrate are investigated. An ordered surface alloy layer composed of 50% Au and 50% Rh is identified as the energetically favored structure, which corresponds to a configuration proposed previously based on scanning tunneling microscopy (STM) imaging [Ovari et al. PCCP 2016, 18, 25230]. Comparing this surface alloy with another candidate structure in terms of Rh and Au adsorption characteristics, the bonding preference among Rh and Au species is recovered. DFT-based simulated STM images reveal bias-voltage-dependent contrast differences among selected corrugated surface layer structures at various Au coverages. Furthermore, several new experimental results obtained by STM and low energy ion scattering (LEIS) on the thermally induced ...