Disentangling Vacancy Oxidation on Metallicity-Sorted Carbon Nanotubes

Pristine single-walled carbon nanotubes (SWCNTs) are rather inert to O$_2$ and N$_2$, which for low doses chemisorb only on defect sites or vacancies of the SWCNTs at the ppm level. However, very low doping has a major effect on the electronic properties and conductivity of the SWCNTs. Already at low O$_2$ doses (80 L), the X-ray photoelectron spectroscopy (XPS) O 1s signal becomes saturated, indicating nearly all the SWCNT's vacancies have been oxidized. As a result, probing vacancy oxidation on SWCNTs via XPS yields spectra with rather low signal-to-noise ratios, even for metallicity-sorted SWCNTs. We show that, even under these conditions, the first principles density functional theory calculated Kohn-Sham O 1s binding energies may be used to assign the XPS O 1s spectra for oxidized vacancies on SWCNTs into its individual components. This allows one to determine the specific functional groups or bonding environments measured. We find the XPS O 1s signal is mostly due to three O-containing functional groups on SWCNT vacancies: epoxy (C$_2$$>$O), carbonyl (C$_2$$>$C$=$O), and ketene (C$=$C$=$O), as ordered by abundance. Upon oxidation of nearly all the SWCNT's vacancies, the central peak's intensity for the metallic SWCNT sample is 60\% greater than for the semiconducting SWCNT sample. This suggests a greater abundance of O-containing defect structures on the metallic SWCNT sample. For both metallic and semiconducting SWCNTs, we find O$_2$ does not contribute to the measured XPS O~1s spectra

LAKE SHOREZONE FUNCTIONALITY INDEX (SFI) A tool for the definition of ecological quality as indicated by Directive 2000/60/CE

www.appa.provincia.tn.it/binary/pat_appa/pubblicazioni/IFP_Manual_english_ver2.1310115028.pd

LAKE SHOREZONE FUNCTIONALITY INDEX (SFI) A tool for the definition of ecological quality as indicated by Directive 2000/60/CE

www.appa.provincia.tn.it/binary/pat_appa/pubblicazioni/IFP_Manual_english_ver2.1310115028.pd

Transfer-free electrical insulation of epitaxial graphene from its metal substrate

High-quality, large-area epitaxial graphene can be grown on metal surfaces but its transport properties cannot be exploited because the electrical conduction is dominated by the substrate. Here we insulate epitaxial graphene on Ru(0001) by a step-wise intercalation of silicon and oxygen, and the eventual formation of a SiO$_2$ layer between the graphene and the metal. We follow the reaction steps by x-ray photoemission spectroscopy and demonstrate the electrical insulation using a nano-scale multipoint probe technique.Comment: Accepted for publication in Nano Letter

Frequency Effect in Fretting Wear of Co-28Cr-6Mo Versus Ti-6Al-4V Implant Alloys

A piezo-electrically driven fretting testing device has been constructed and fretting release and release rates have been determined with highest accuracy using a radio tracer technique. First results on the fretting release and release rate of titanium alloy fretting pads against Cobalt-chrome alloy fatigue specimens are reported. The frequency dependency of fretting release has been determined between 1 Hz and 8 Hz and shows higher release rates for low frequencies, thus indication that accelerated testing of materials and components of artificial joints must be analyzed extremely carefully. The present experiments under simple conditions present a base-line study for step-wise applying more complex and realistic testing conditions and for using radio tracer methods to quantify fretting release in simulated testing of artificial hip- and knee-prostheses.JRC.I.4-Nanotechnology and Molecular Imagin

A Compact Fretting Device for Testing of Biomaterials by Means of Thin Layer Activation

Thin layer activation has been applied to measure fretting wear release of medical grade Ti-6Al-4V in the sub-micro gram range and wear rates in the order of magnitude of 10-7 ng/cycle. Thin layer activation allows to define an area of interest by local irradiation and avoids artefacts of fretting effects on specimen grips or elsewhere. The aim of the paper is to demonstrate the suitability of thin layer activation for quantitative measurements of very small material quantities released during fretting experiments. For the present experiments a piezo-electrically driven fretting device is presented that is sufficiently to comply with space restrictions and the requirements of working in a radiation protected environment. The equipment and the applied methodology is described and first results on two sets of experiments of semi-spherical samples fretted against a flat fatigue sample machined form Ti-6Al-4V are presented. Both set of experiments where conducted under nominally identical parameters, the only variation consisting in different surface finishes of the fatigue samples.JRC.I.4-Nanotechnology and Molecular Imagin

The Effect of Surface Treatments on the Fretting Behaviour of Ti-6Al-4V Alloy

Stem modularity in total hip replacement introduces an additional taper joint between Ti-6Al-4V stem components with the potential for fretting corrosion processes. One possible way to reduce the susceptibility of the Ti-6Al-4V / Ti-6Al-4V interface to fretting is the surface modification of the Ti-6Al-4V alloy. Among the tested, industrially available surface treatments, a combination of two deep anodic spark deposition treatments followed by barrel polishing resulted in a four times lower material release with respect to untreated, machined fretting pad surfaces. The fretting release has been quantified by means of radiotracers introduced in the alloy surface by proton irradiation. In a simple sphere on flat geometry, the semispherical fretting pads were pressed against flat, dog-bone shaped Ti-6Al-4V fatigue samples cyclically loaded at 4 Hz. In this way a cyclic displacement amplitude along the surfaces of 20 μm has been achieved. A further simplification consisted in the use of deionized water as lubricant. A comparison of the radiotracer results with an electrochemical material characterization after selected treatments by potentiostatic tests of modular stems in 0.9% NaCl at 40°C for ten days confirmed the benefit of deep anodic spark deposition and subsequent barrel polishing for improving the fretting behaviour of Ti-6Al-4V.JRC.I.4-Nanobioscience