On the traceably accurate voltage calibration of electrostatic accelerators

We describe in detail a calibration method for the terminal voltage of small accelerators used for ion beam analysis, with the elastic resonance of 16O(α,α)16O at 3038 keV as the intrinsic measurement standard. The beam energy relative to this resonance is determined with a precision around 300 eV and an evaluated reproducibility of 1.0 keV. We show that this method is both robust and convenient, and demonstrate consistency with calibration relative to three other independent methods: using radioactive sources and using the resonant 27Al(p,γ)28Si and non-resonant 16O(p,γ)17F direct capture reactions. We re-evaluate the literature and show that the peak in the cross-section function is at 3038.1 ± 2.3 keV. By comparing the results obtained with 16O(α,α)16O to the other calibration methods we show that this uncertainty can be reduced to 1.3 keV.</p

Formation of carbon nitride nanospheres by ion implantation

Carbon nitride nanospheres have been synthesized into copper by simultaneous high fluence (10 at. cm) implantations of C and N ions. The composition of the implanted region has been measured using C(d,p)C and N(d,α)C nuclear reactions induced by a 1.05 MeV deuteron beam. The C and N depth profiles are very close and the retained doses into copper are relatively high, which indicates that carbon and nitrogen diffusion processes are likely limited during implantation. High resolution transmission electron microscopy (HRTEM) observations and electron diffraction (ED) analyses have been carried out to determine the structure of the nanospheres formed during implantation. Some consist in small hollow amorphous nanocapsules with sizes ranging from 30 to 100 nm. Large gas bubbles with diameters up to 300 nm have also been observed in the copper matrix. Electron energy-loss spectroscopy (EELS) measurements performed on the small nanocapsules indicate that their shells are composed of carbon and nitrogen. © 2007 Elsevier B.V. All rights reserved

Development of nanotopography during SIMS characterization of thin films of Ge1−xSnx alloy

This work presents a study of application of secondary ion mass spectrometry (SIMS) to measure tin concentration in Ge1−xSnx alloy with x higher than solid solubility ∼1%, i.e. well above the diluted regime where SIMS measurements usually provide the most reliable quantitative results. SIMS analysis was performed on Sn+ ion implanted Ge films, epitaxially deposited on Si, and on chemical vapordeposition deposited Ge0.93Sn0.07 alloy. Three SIMS conditions were investigated, varying primary beam ion species and secondary ion polarity keeping 1 keV impact energy. Best depth profile accuracy, best agreement with the fluences measured by Rutherford backscattering spectrometry, good detection limit(∼1 × 1017at/cm3) and depth resolution (∼2 nm/decade) are achieved in Cs+/SnCs+ configuration. However, applied sputtering conditions (Cs+1 keV, 64° incidence vs. normal) induced an early formation of surface topography on the crater bottom resulting in significant variation of sputtering yield. Atomic force microscopy shows a peculiar topography developed on Ge: for oblique incidence, a topography consisting in a sequence of dots and ripples was observed on the crater bottom. This behavior is unusual for grazing incidence and has been observed to increase with the Cs+fluence. Rotating sample duringsputtering prevents this ripple formation and consequently improves the depth accuracy

Adsorption of titanium dioxide nanoparticles onto zebrafish eggs affects colonizing microbiota

Teleost fish embryos are protected by two acellular membranes against particulate pollutants that are present in the water column. These membranes provide an effective barrier preventing particle uptake. In this study, we tested the hypothesis that the adsorption of antimicrobial titanium dioxide nanoparticles onto zebrafish eggs nevertheless harms the developing embryo by disturbing early microbial colonization. Zebrafish eggs were exposed during their first day of development to 2, 5 and 10 mg TiO2 L−1 (NM-105). Additionally, eggs were exposed to gold nanorods to assess the effectiveness of the eggs’ membranes in preventing particle uptake, localizing these particles by way of two-photon microscopy. This confirmed that particles accumulate onto zebrafish eggs, without any detectable amounts of particles crossing the protective membranes. By way of particle-induced X-ray emission analysis, we inferred that the titanium dioxide particles could cover 25–45 % of the zebrafish egg surface, where the concentrations of sorbed titanium correlated positively with concentrations of potassium and correlated negatively with concentrations of silicon. A combination of imaging and culture-based microbial identification techniques revealed that the adsorbed particles exerted antimicrobial effects, but resulted in an overall increase of microbial abundance, without any change in heterotrophic microbial activity, as inferred based on carbon substrate utilization. This effect persisted upon hatching, since larvae from particle-exposed eggs still comprised higher microbial abundance than larvae that hatched from control eggs. Notably, pathogenic aeromonads tolerated the antimicrobial properties of the nanoparticles. Overall, our results show that the adsorption of suspended antimicrobial nanoparticles on aquatic eggs can have cascading effects across different life stages of oviparous animals. Our study furthermore suggests that aggregation dynamics may occur that could facilitate the dispersal of pathogenic bacteria through aquatic ecosystems.</ul

Study of carbon nitride compounds synthesised by co-implantation of 13C and 14N in copper at different temperatures

Carbon nitride compounds have been synthesised in copper by simultaneous high fluence (1018 at. cm−2) implantation of 13C and 14N ions. During the implantation process, the substrate temperature was maintained at 25, 250, 350 or 450 °C. Depth profiles of 13C and 14N were determined using the non-resonant nuclear reactions (NRA) induced by a 1.05 MeV deuteron beam. The retained doses were deduced from NRA measurements and compared to the implanted fluence. The chemical bonds between carbon and nitrogen were studied as a function of depth and temperature by X-ray photoelectron spectroscopy (XPS). The curve fitting of C 1s and N 1s core level photoelectron spectra reveal different types of C–N bonds and show the signature of N2 molecules. The presence of nitrogen gas bubbles in copper was highlighted by mass spectroscopy. The structure of carbon nitride compounds was characterised by transmission electron microscopy (TEM). For that purpose, cross-sectional samples were prepared using a focused ion beam (FIB) system. TEM observations showed the presence of small amorphous carbon nitride “nano-capsules” and large gas bubbles in copper. Based on our observations, we propose a model for the growth of these nano-objects. Finally, the mechanical properties of the implanted samples were investigated by nano-indentation

Regular nano-void formation on Ge films on Si using Sn ion implantation through silicon nitride caps

Germanium is known to present a peculiar lattice damage evolution under heavy mass ion irradiation. In fact, a characteristic ‘honeycomb-like’ void structure is formed once a threshold fluence is implanted (typically 5-10E1014 at/ cm2). The structure consists of a relatively regular network of columnar voids, with ~10 nm diameter and ~100 nm depth. The different diffusivity of self-interstitials and vacancies and vacancy agglomeration are thought to be the mechanisms responsible for the phenomenon. In this work we tried to use Silicon nitride (SiN) caps of different thickness to act on void formation and to prevent contamination in the nano-voids. The starting wafers had a Germanium 1.5 μm thick film CVD epitaxially deposited on (100) Si substrates. A 5E15 at/ cm2 Sn+ fluence was implanted on three different samples: no cap on Ge surface, 11 nm of SiN cap on Ge and 20 nm SiN on Ge. The implant energy was adjusted to have the same Sn (and damage) distribution in Ge despite the different SiN cap thicknesses. Sample surfaces were characterized by SEM and AFM. Cross section TEM provided information about the development in depth of the voids. SIMS and RBS were used to obtain information about final Sn and contaminant distribution and the damaged layer thickness. X-ray photoelectron spectroscopy (XPS) was used to identify contaminants and degree of oxidation of Ge and Sn atoms. Results about the obtained void geometry will be reported and formation mechanisms will be discussed