| Surface elastic properties of Ti alloys modified for medical implants: A force spectroscopy study. |
| C. Munuera, T.R. Matzelle, N. Kruse, M.F. Lopez, A. Gutierrez, J. A. Jimenez, C. Ocal |
| Acta Biomaterialia 3 (2007) 113119. |
| We report here the first nanoscale surface elasticity measurements on surface-modified titanium alloys using the force spectroscopy mode in scanning force microscopy. Samples of three vanadium-free titanium alloys, Ti7Nb6Al, Ti13Nb13Zr and Ti15Zr4Nb, were investigated. Surface modification of the three alloys was produced by thermal oxidation in air at 750 ° C for different times, which resulted in the formation of protective oxide layers with different surface composition and morphology. The elastic properties of the surface layers were studied comparatively in the as-received Ti alloys and after the oxidation process using cantilevers with different stiffness to evaluate the influence of the indentation depth. In all cases, Youngs modulus of the sample surfaces was found to be lower than 65 GPa, and as low as 20 GPa for some of the oxidized samples. Variations observed for the three oxidized Ti alloys can be related to the different chemical composition of the outer layers generated for the different oxidation times. |
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| Temperature-dependent modifications in the surface composition of Finemet: A ToF-SIMS study. |
| Chenakin, S. P.; Vasylyev, M. A.; Galstyan, G. G.; Kruse, N. |
| Institute of Metal Physics, National Academy of Sciences of Ukraine, Blvd. Akademik Vernadsky 36,Department of Atomic Structure and Surface Dynamics, 03680,Kiev,Ukraine.Surface Science(2006),600(17),3394-3402.Publisher: Elsevier B.V.,CODEN: SUSCASISSN: 0039-6028.Journalwritten in English.AN 2006:927642CAPLUS |
| Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was employed as an in situ tool to study the temp.-induced alteration of the surface compn. of amorphous Finemet, Fe73Si15.8B7.2Cu1Nb3. Temp. was changed reversibly by cooling from room temp. to 118 K and warming back to room temp.As a general result, the ion intensities and, consequently, the surface concns. of the alloy constituents were found to vary non-monotonously.Therefore segregation processes were in operation the extent of which was element-specific.Most importantly, while cycling the temp. hysteresis behavior was obsd. with concn. of Fe developing just opposite to that of the alloying elements.Accordingly, on cooling the alloy, the surface enrichment with B, Si, Nb, Cu attained first a max. in the range of 248-193 K before the segregation changed the trend to establish appreciable depletion of these elements at 118 K (as compared to room temp.).By contrast, the surface iron content developed inversely and decreased first to a min. at .apprx. 223 K before reaching enrichment at 118 K. During warming, a max. segregation of boron and silicon was obsd. at about 223 K - similar as on cooling - so that this temp. can be considered characteristic of the segregation process.Dissociative adsorption of water from the residual atm. occurring at low temps. was responsible for the formation of surface hydroxides of iron, silicon and niobium; an enhanced adsorption of mol. water was obsd. at temps. below 153 K. The temp.-dependent segregation and adsorption-desorption processes were found to be largely reversible, so that the surface compn. of Finemet was practically restored after finishing the cooling-warming cycle.The processes and factors governing the non-monotonous temp. dependence of the surface segregation in the amorphous alloy are discussed within the frame of segregation theory and the influence of temp.-induced tensile stress on segregation. |
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| Oxygen adsorption on gold nanofacets and model clusters. |
| Visart de Bocarme, T.; Chau, T.-D.; Tielens, F.; Andres, J.; Gaspard, P.; Wang, R. L. C.; Kreuzer, H. J.; Kruse, N. |
| Chemical Physics of Materials,Universite Libre de Bruxelles, Brussels,Belg.Journal of Chemical Physics(2006),125(5),054703/1-054703/7.Publisher: American Institute of Physics,CODEN: JCPSA6ISSN: 0021-9606.Journalwritten in English.AN 2006:810624CAPLUS |
| We have studied O interaction with Au crystals (field emitter tips) using time-resolved (atom-probe) field desorption mass spectrometry.The results demonstrate no adsorption to take place on clean Au facets under chosen conditions of pressures (p<10-4 mbar) and temps. (T = 300-350 K).Steady elec. fields of 6 V/nm do not allow dissocg. the O mol.The measured O2+ intensities rather reflect ionization of O2 mols. at crit. distances above the Au tip surface.Certain amts. of Au-O2 complex ions can be found at the onset of Au field evapn.Calcns. by d. functional theory (DFT) show weak O end-on interaction with Au10 clusters (DE = 0.023 eV) and comparatively stronger interaction with Au1/Au(100) model surfaces (DE = 0.25 eV). No binding is found on {210} facets.Including (pos.) elec. fields in the DFT calcns. leads to an increase of the activation energy for O dissocn. thus providing an explanation for the absence of at. O ions from the field desorption mass spectra. |
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| Field-induced CO adsorption and formation of carbonyl waves on gold nanotips. |
| Visart de Bocarme, T.; Kruse, N.; Gaspard, P.; Kreuzer, H. J. |
| Chemical Physics of Materials, Universite Libre de Bruxelles, Brussels,Belg. Journal of Chemical Physics(2006),125(5),054704/1-054704/6.Publisher: American Institute of Physics,CODEN: JCPSA6ISSN: 0021-9606.Journalwritten in English. AN 2006:810623CAPLUS |
| We report a study of the adsorption and reaction of CO on a Au nanotip in high electrostatic fields. Field ion microscopy is used to investigate the emergence of a Au-carbonyl wave that is made visible with O as the imaging gas. We set up a simple kinetic model that reproduces the adsorption wave and confirms that the presence of O merely serves as an imaging gas and does not lead to field-induced oxidn. of CO. |
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| XPS and ToF-SIMS characterization of a finemet surface: effect of cooling. |
| Chenakin, S. P.; Vasylyev, M. A.; Kruse, N.; Tolstogouzov, A. B. |
| Institute of Metal Physics, National Academy Sciences of Ukraine, Kiev, Ukraine. Surface and Interface Analysis(2006), 38(7), 1164-1172. Publisher : John Wiley & Sons Ltd.,CODEN: SIANDQISSN : 0142-2421. Journalwritten in English. AN 2006:757238CAPLUS |
| The surface compn. of amorphous Finemet, Fe73Si15.8B7.2Cu1Nb3, was studied by XPS and time-of-flight secondary ion mass spectrometry (ToF-SIMS).The as-received sample in the original state and after Ar+ sputter-cleaning was analyzed at room temp. as well as after cooling to -155°C. In the cooled state, the surface oxide layer composed of oxides of the alloy constituents was found to become enriched with elemental iron and depleted of elemental silicon, boron, oxygen and carbon as compared to the state at room temp. Interaction of residual water vapor and hydrogen with the complex oxide layer occurring at low temps. is believed to be responsible for the enhanced formation of surface hydroxides of the alloy constituents.The processes resulting in the obsd. redistribution of the elements on the surface of Finemet at low temps. are discussed. |
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