Search

Interaction of acid and acid+alkali treated titanium samples with simulated body fluid was studied. In case of alkali treated titanium, the dynamic arrangement of the test enabled the detection of primary calcium and phosphate ion adsorption from the solution and later apatite crystal growth (XRD). The induction time for crystal growth was 24.2±0.3 h. On acid-only treated titanium no crystal growth was detected. The calcium phosphate adsorption layer formed on the acid treated samples was detectable by XPS only, however it differed from that one formed on the acid+alkali treated samples. The adsorption layer formed on the acid+alkali treated samples contained larger amount of calcium, especially in the shortest exposure times. Charging of the apatite crystallites during the XPS measurement enabled the determination their Ca/P ratio separately from Ca/P ratio of the adsorption layers. XPS and EDS analyses indicated that the spherulitic crystallites consisted of carbonated hydroxyapatite with the Ca/P ratio close to that one of the stoichiometric hydroxyapatite. It is proposed that the adsorption layer formed spontaneously and immediately on the acid+alkali treated titanium can provide an ideal interface between the metal implant and the apatite cement line, the first structure formed by osteoblast cells during the formation of the new bone on foreign surfaces.

Pd x Co 1− x thin layers with different stoichiometry, prepared by DC magnetron sputtering on α -Al 2 O 3 (sapphire) substrates, were investigated by X-ray photoelectron spectroscopy (XPS), static secondary ion mass spectroscopy (SSIMS) and temperature programmed desorption (TPD). The shifts of Pd 3d, XPS Auger Pd-MNN and the valence-band centre toward higher binding energies due to the formation of a bimetallic bond were observed. CO adsorption properties of the alloys were strongly dependent on alloy stoichiometry. The common property was the lowering of the CO desorption temperature with respect to the desorption from pure metals. The SSIMS study showed that CO partially dissociated on Co–Pd alloy surfaces.

In2O3 belongs to the group of metal oxides used successfully for gas detection, with sensitivity for CO and H2 comparable with that of SnO2 and excellent for O3. The sensing properties of these sensors could be greatly improved by adding small amount of transition metals such as Pd, Pt, Au, etc. In this work, we used X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) to study the growth of Pd particles on In2O3 substrates prepared by spray pyrolysis method. Surface stoichiometry and its changes during Ar+ ion bombardment used for surface cleaning were checked with XPS and ISS. The Pd growth was studied stepwise in situ using the micro-electron beam evaporation source (MEBES) with controlled evaporation rate. XPS and ISS measurements were carried out with special attention to metal–substrate interaction (MSI), which was observed for Pd–In and resulted in the formation of Pd–In alloy with noble metal-like electronic structure. Further, we studied reduction of these samples after oxidation in air. A lower reduction temperature than with bulk PdO was observed. The results are compared with the experiment of Pd deposition performed on a pure In foil.

The nature of the bonding between Pd atoms and alumina surfaces was investigated by analysing the oxygen photoelectron induced Auger KLL transitions. The activity of oxide surfaces was analysed in terms of the surface ability for electronic exchange with the metal adlayer. The comparative study of the metal–substrate interaction on different types of Pd supports (α-Al 2 O 3 , γ-Al 2 O 3 and thin alumina layers on polycrystalline Al foil) is presented in this paper. The surface atomic composition of all substrates after cleaned bombardment procedure was determined by ion scattering spectroscopy. The ionicity of the oxygen sites was observed to be a function of the oxide thickness and stoichiometry. It was found that the reduction of the oxide surfaces caused the increase of the I (KL 23 L 23 )/ I (KL 1 L 23 ) intensity ratio, i.e. the increase of the ionicity. The opposite tendency for this ratio was observed during Pd deposition on thin alumina oxide. The possible explanations of such behaviour (charge transfer to Pd particle and/or creation of the Al–Pd alloy) are discussed.

The metal–substrate interaction (MSI) represents an important effect determining the properties of supported heterogeneous catalysts. We investigated the MSI effects by X-ray photoelectron spectroscopy, ion scattering spectroscopy and thermal desorption spectroscopy in the case of Pd films vapor deposited on non-stoichiometric aluminum oxide substrates. We compared the obtained results with these of bulk Pd and Pd/Al reference alloy. The observed MSI is explained by the formation of an intermetallic interface exhibiting a strong bimetallic transition-metal (Pd)/s, p-metal (Al) interaction. The fundamental studies of Pd/Al bimetallic alloys are of an importance due to the role that they play in the modification of chemisorption and catalytic properties of real Pd/Al-oxide systems as well as in the realization of novel Pd-alloy catalysts. The reported behavior represents a new way in explanation of former unexpected CO adsorption properties of alumina supported Pd particles.

In the first part, thicknesses and spectral dependences of the optical constants of the diamond like carbon (DLC) films were determined without any parameterization in the range 240–830 nm by multi-sample modification of variable angle spectroscopic ellipsometry (VASE). DLC films were prepared by plasma enhanced chemical vapor deposition (PECVD) onto silicon single crystal substrates. It was shown that the influence of some defects of the DLC films on the optical constants is suppressed by applying the method of multi-sample modification of VASE. In the second part, the spectral dependences of the determined optical constants were interpreted using a recently developed model of dispersion based on the modified Lorentz oscillator. Two modified Lorentz oscillators corresponding to both π→π* and σ→σ* interband transitions were taken into account. Within this model of dispersion of the optical constants, the concept of the band gap and the existence of localized energy states within the band gap were taken into account as well.

X-ray photoelectron spectroscopy and ion-scattering spectroscopy (ISS) were used to investigate the interaction of palladium with reduced thin-film alumina. The substrate was prepared by Ar+ ion bombardment thinning of the natural oxide layer on polycrystalline aluminum foil. It was found that the constitution of a surface equilibrium is determined by the energy of sputtering ions. Therefore, after the sputtering, the aluminum oxide surface is covered by more or less Al0-rich overlayer. During the first stage of the Pd deposition, the IAl/IO ratio decreases because of Pd atom deposition onto the Al sites, keeping the anionic oxygen sites unaffected. With increasing Pd, the PdAl intermetallic compound is formed. The alloy forms three-dimensional clusters and a bare alumina surface appears, giving the ISS intensity ratio IAl/IO characteristic for γ-Al2O3. At a high amount of deposited Pd, the Pd bulk-like phase is formed, gradually burying the PdAl alloy clusters. To interpret catalytic behavior of Pd/Al2O3 systems, the presence of the PdAl alloy caused by strong metal–substrate interaction should be considered.

The sensitivity and selectivity of SnO2 based gas sensors could be improved by doping of small amount of transition metals. In this work we used X-ray photoelectron spectroscopy, ion scattering spectroscopy, and thermal desorption techniques to investigate Pd evaporated on SnOx thin layer substrate, prepared by spray pyrolysis. The evolution of Pd/SnOx layer morphology with increasing amount of Pd deposits was studied using the XPS inelastic background shape analysis. The observations are compared to the results obtained from natural SnO2 crystal and metallic Sn substrates. A strong Pd–Sn bimetallic interaction was observed, resulting in the formation of PdSn alloy of noble metal-like electronic structure. This feature also corresponds to the presence of two CO desorption states with low energy peaks at approximately 390 K. The relation of our results with the operation mechanism of gas detection are discussed.

Diamond-like carbon (DLC) films were prepared by plasma-enhanced chemical vapour deposition from the mixture of methane and argon on silicon substrates. Films were characterised by multi-sample modification of variable angle spectroscopic ellipsometry. Ellipsometry showed that there is a transition interlayer between the DLC film and the silicon substrate that cannot be attributed to a thin silicon dioxide layer but rather to amorphous silicon and/or a modified oxide layer. TRIM calculations revealed that argon or carbon ions could not produce a significant layer of amorphous silicon because the depth of target atom displacements is below the thickness of a native oxide layer. The chemical composition of a DLC film profile including a DLC/silicon interface was studied by X-ray photoelectron spectroscopy (XPS) coupled with argon sputtering of the 34 nm thick DLC film. The DLC/silicon interface composed of less than 6% of oxygen and a gradually decreasing and increasing carbon and silicon percentage, respectively.

The metal–substrate and metal–metal interactions represent important effects determining the properties of supported catalysts. We investigate the CO adsorption mechanism on Pd particles supported on Al 2 O 3 and Al by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). CO–metal interaction is investigated by TP desorption of CO and by XPS of C 1s intensities that exhibit three CO-related components. The dissociation activity is monitored as a rise of C 1s signal at 285 eV while the molecularly adsorbed CO exhibits the intensity at 287 eV. Pd–substrate interaction is determined from the Pd core- and valence-level binding energy variations. The influence of the Pd–Al alloying process on the Pd MNN Auger transition is shown. The studies show that the metal–substrate and metal–metal interactions play an important role in CO–Pd adsorption process.

The metal–substrate interaction (MSI) represents one of the most important effects determining the properties of supported catalysts. It is expected to be one of the driving forces of the size effect in catalysis. In this work we investigated the MSI by X-ray photoelectron spectroscopy (XPS) in the case of small Pd particles deposited on γ- and α-alumina substrates. We compared the binding energy and initial state variations as a function of Pd coverage. The initial state has been found to be shifted to higher positive values for a more strongly interacting substrate (γ-Al2O3), whilst for the inert-like sapphire substrate the MSI was less important. The initial state shift value was associated with the electron transfer in the substrate clusters direction. It was shown that the substrate–metal charge transfer could be responsible for partial CO dissociation on γ-Al2O3 supported Pd particles.

The adsorption of carbon monoxide on small alumina-supported Pd particles have been studied by X-ray photoelectron spectroscopy (XPS). The results showed clearly different surface properties of bulk metal and supported clusters. The effect of partial CO dissociation was observed on Pd deposited on γ-alumina and on clean aluminium, but not on small Pd particles prepared on thin amorphous oxide film on Al substrate. CO–Pd interaction was determined from C 1s photoelectron spectra that exhibited two CO-related components. The dissociation activity was monitored as a rise of C 1s signal at 285 eV, while the molecularly adsorbed CO exhibited the intensity at 287 eV. The study showed that beside the particle size, the metal–substrate interaction (MSI) plays an important role in CO–Pd adsorption process.

The interaction of oxygen with gold adsorbed on Ti(0001) was studied by synchrotron radiation photoelectron spectroscopy. Two kinds of surfaces were explored: as-deposited 0.38, 1.16 and 1.85 monolayer (ML) thick Au overlayers on the Ti(0001) surface, and the same samples after thermal treatment, which resulted in the formation of Au-Ti intermetallic surfaces. The Ti 3p core level was strongly affected by reaction with oxygen, while the Au 4f core level showed only minor changes other than a decrease in intensity. The Ti 3p peak was fitted with several components which were identified as Ti atoms in different oxidation states, namely TiO, Ti(2)O(3), TiO(2) and Ti-OH. Titanium oxide phase formation is accompanied by Au-Ti bond dissociation and outward diffusion of Ti. The presence of an Au-Ti intermetallic phase on the Ti(0001) surface promotes oxidation of the Ti atoms.

Submonolayer coverage of Sn on a Pt(110) surface was studied by photoemission and low-energy electron diffraction. Deposition of less than 0.6 ML at 300 K gives rise to a c(2 × 2) surface reconstruction with weak diffraction spots at the very beginning of growth, and no other LEED patterns were found at this temperature. A new (4 × 1) Sn/Pt(110) surface structure was observed after flashing to 570 K a coverage of 0.64 ML. The total Sn coverage decreased to 0.58 ML after flashing as some of the atoms diffused into deeper layers. Different Sn phases were identified on the (4 × 1) Sn/Pt(110) surface: two types of surface Sn atoms in different adsorption sites, a subsurface Sn-Pt intermetallic layer and Sn-Pt surface islands. To investigate chemical reactivity, 0.25 ML Sn/Pt(110) and 0.58 ML (4 × 1) Sn/Pt(110) surfaces were exposed to 1000 L of O(2) at 300 K. Analyses of the photoemission data provide evidence for the formation of tin oxide. The interaction with oxygen of the two surfaces is similar, independent of surface structure and the composition of the subsurface layers. The Sn concentration in the interface intermetallic layer is the main factor which influences the oxygen adsorption.

An outstanding question regarding the probing or possible device applications of correlated electronic materials (CEMs) with layered structure is the extent to which their bulk and surface properties differ or not. The broken translational symmetry at the surface can lead to distinct functionality due to the charge, lattice, orbital, and spin coupling. Here we report on the case of bilayered manganites with hole doping levels corresponding to bulk ferromagnetic order. We find that, although the hole doping level is measured to be the same as in the bulk, the surface layer is not ferromagnetic. Further, our low-energy electron diffraction and x-ray measurements show that there is a c-axis collapse in the outermost layer. Bulk theoretical calculations reveal that, even at fixed doping level, the relaxation of the Jahn-Teller distortion at the surface is consistent with the stabilization of an A-type antiferromagnetic state.

We have studied the adsorption of low dimensional gold on ceria, produced by evaporation onto the surface. The interaction of gold with CeO(2)(111) layers was investigated with x-ray photoemission spectroscopy, ultraviolet photoemission spectroscopy, and resonant photoelectron spectroscopy (RPES). Gold was deposited in steps onto a 1.5 nm thick CeO(2)(111) layer epitaxially grown on a Cu(111) substrate. The RPES showed a partial Ce(4+)--Ce(3+) reduction, observed as a resonant enhancement of the 4f level of the Ce(3+) species. This can be explained by possible creation of a new Au(+) ionic state. The observed effects are stronger for Au deposition at room temperature than at 250 degrees C. The obtained results are in agreement with already published density functional theory calculations reporting weakening of bond between the oxygen and the Ce atoms in ceria caused by the presence of gold.

$\mathrm{Pb}∕\mathrm{Ni}(111)$ surface phases were investigated by angle-resolved photoemission spectroscopy. Annealing of the $\mathrm{Pb}∕\mathrm{Ni}(111)$ surface led to the formation of the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ reconstruction characterized by a topmost layer consisting of a substitutional alloy. The transformation to the $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ structure was accompanied by a modification of the surface band structure confirming the formation of a new phase in the Ni(111) surface layer, characterized by a transformation from ferromagnetic to a nonmagnetic state. The modification was displayed as a disappearance of the $\mathbit{k}$-dependent exchange splitting in the topmost alloy layer that was observed on the clean Ni surface due to the energy difference between spin-up and spin-down states. Fermi surface mapping showed partial disappearance of splitting of bands crossing the Fermi level.

The reaction of oxygen at low pressure with the Sn/Pd(110) system has been examined by photoelectron spectroscopy using synchrotron radiation. The c(2 × 2) and (3 × 1) reconstructions of the Sn/Pd(110) surface at 0.5 and 0.7 monolayers (ML) Sn coverage and a 1.75 ML Sn overlayer on the Pd(110) surface after flashing to 470 K were studied. The Sn 4d core level is strongly affected by O(2) adsorption while the Pd 3d core level shows very little change other than a decrease in intensity. Starting with a 10 L dose of oxygen, prominent changes in the spectra were observed for all Sn/Pd(110) surface alloys. Analysis of the Sn 4d core levels indicates that oxidation proceeds with the formation of well-defined states of Sn, which were identified as a Pd-Sn-O interface layer, SnO and SnO(2) oxides. The valence band spectra confirm this assignment. The Sn(2+) and Sn(4+) component signals originate from the topmost surface layer, i.e. tin atoms in more highly oxidized states constitute the topmost surface layer on top of the Pd-Sn-O interface. The presence of a sub-surface PdSn intermetallic alloy facilitates the tin oxide formation; the Sn-O phase formation is accompanied by Pd-Sn bond dissociation.