17 research outputs found
H-terminated polycrystalline boron doped diamond electrode for geochemical sensing into underground components of nuclear repositories
Nuclear waste repositories are being installed in deep excavated rock formations in some places in Europe to isolate and store radioactive waste. In France, Callovo-Oxfordian formation (COx) is potential candidate for nuclear waste repository. It is thus necessary to measure in situ the state of a structure's health during its entire life. The monitoring of the near-field rock and the knowledge of the geochemical transformations can be carried out by a set of sensors for a sustainable management of long-term safety, reversibility and retrievability. Among the chemical parameters, the most significant are pH, conductivity and redox potential. Wide band gap semiconductors are favored materials for chemical sensing because of their high stability to many chemical agents. Among the wide band gap materials, Chemical Vapor Deposition (CVD) boron doped diamond (BDD) benefits from a large band gap (5.45 eV), which gives rise to a wide electrochemical potential window (~3 V/Saturated Calomel Electrode(SCE)) (Angus et al. 1999). It is moreover described as a radiation, corrosion and bio-corrosion resistant. These remarkable properties, in addition to a low double layer capacity and a low residual current, make BDD a promising material for geochemical sensor elaboration. This work aimed to investigate BDD- based electrodes coated with p-type polycrystalline BDD- hydrogen-terminated surfaces (1 cm2) for pH and/or redox measurements into the underground components of nuclear repositories. The boron-doped p-type channel was grown in a microwave plasma reactor (BJS 150) (Silva et al. 2009). The boron-doped channel was hydrogen terminated by a hydrogen plasma treatment in the CVD reactor, resulting in full saturation of the surface carbon bonds with hydrogen atoms. Figure 1 shows the Scanning Electron Microscopy (SEM) of the polycrystalline BDD coating with a Bore/Carbon ratio of 500 ppm and its Raman spectrum. SEM micrograph illustrates the typical columnar growth of the polycrystalline CVD diamond. A homogeneous surface was observed concerning the crystallite size which average was 1.5 microns. On the Raman spectrum of a single crystal diamond intrinsic film (undoped), the diamond peak is usually observed at 1332 cm-1. In Figure 1, the intense peak at 1327 cm-1 corresponding to diamond is shifted due to the "Fano" effect according to doping, which is observed through a broad peak at 910 cm-1. Its intensity shows that the investigated sample was highly doped. Gheeraert et al. (1993) suggested that the peaks at 500 and 1230 cm-1 appears when the boron concentration reaches the critical value of 3×1020 at.cm-3 corresponding to a metallic conductivity. The lack of peak around 1350 cm-1 and 1570 cm-1, which corresponds respectively to D and G graphite peak of impurity phases of non-diamond carbon (sp2), attests to the crystalline quality of the deposit. The slight width at half maximum of the characteristic peak of diamond compared to that of natural diamond reflects the degree of organization and structural perfection of this phase indicating that the coating was of high quality. Electrodes made in this way have been used for 8 month without any surface treatments or conditioning. The electrochemical behavior of Hydrogen-terminated BDD was studied by cyclic voltammetry. Electrodes showed a wide potential range of about 2 V/SCE. They also showed and a rapid reversible charge transfer in the presence of redox probes such FeCN63-/4- and Ru(NH)63+/2+. Performances, reliability and robustness for pH or redox monitoring were examined by potentiometric measurements at 25°C under anaerobic conditions (oxygen-free atmosphere, 100 % nitrogen) in a glove box. Investigation has been limited in pH, ranging from 5.5 to 13.5, close to those encountered in the environment of the nuclear repositories. The feasibility of measuring pH with BDD electrodes was first tested in NH4Cl/NH3-NaCl (0.1mol L-1) buffer solutions, leading to electrode calibration over the widest range of pH, from around neutral to basic pH. Experiments were also conducted in NaHCO3/Na2CO3 buffer samples, similar to conditions prevailing in the COx formation. For redox measurements, [Fe3+]/[Fe2+] ratios were analysed at different pH and/or ionic strengths (supporting electrolytes concentration ranged from 0.05 to 1 mol.L-1). The same measurements were also done using a 10-mm disk platinum electrode with a surface of 78.54 mm². No pH sensitivity was observed, thus the energy level of the state was not moved. However, for redox measurements the potential acquired by Hydrogen-terminated BDD and Platinum electrode converged to a value of the same order of magnitude, independently of the sample. This fact demonstrates that, under the same experimental conditions, the redox couples fixe identically the potential of the electrodes. Investigations with reference to ionic strength in thermodynamically equilibrated Fe(III)/Fe(II) samples were highly interesting. Independently of the electrode, the voltage measurement was not or little affected, whereas both the solution conductivity as well as the speciation were affected, due to the increase in salinity. This means that the term [Fe3+]/[Fe2+] is practically unaffected. This implies that assuming the ratio of the activity coefficients, γFe3+/ γFe2+ as equal to 1 has a minor effect on the measured redox potential. H-terminated BDD electrode appears well suited for redox monitoring. Work is in progress to demonstrate the robustness of the H-terminated BDD electrode for redox monitoring into COx over a long period
Personal Health Train on FHIR:A Privacy Preserving Federated Approach for Analyzing FAIR Data in Healthcare
Big data and machine learning applications focus on retrieving data on a central location for analysis. However, healthcare data can be sensitive in nature and as such difficult to share and make use for secondary purposes. Healthcare vendors are restricted to share data without proper consent from the patient. There is a rising awareness among individual patients as well regarding sharing their personal information due to ethical, legal and societal problems. The current data-sharing platforms in healthcare do not sufficiently handle these issues. The rationale of the Personal Health Train (PHT) approach shifts the focus from sharing data to sharing processing/analysis applications and their respective results. A prerequisite of the PHT-infrastructure is that the data is FAIR (findable, accessible, interoperable, reusable). The aim of the paper is to describe a methodology of finding the number of patients diagnosed with hypertension and calculate cohort statistics in a privacy-preserving federated manner. The whole process completes without individual patient data leaving the source. For this, we rely on the Fast Healthcare Interoperability Resources (FHIR) standard
Reduction of dislocation densities in single crystal CVD diamond by confinement in the lateral sector
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Thick heavily boron doped CVD diamond films homoepitaxially grown on (111)-oriented substrates
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Improvement of dislocation density in thick CVD single crystal diamond films by coupling H 2 /O 2 plasma etching and chemo-mechanical or ICP treatment of HPHT substrates
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High quality thick CVD diamond films homoepitaxially grown on (111)-oriented substrates
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Renseignement du statut tabagique dans un système d’information hospitalier : une étude observationnelle à partir de l’entrepôt de données cliniques de l’Hôpital Européen Georges Pompidou, Paris, France
Pulsed DC bias for the study of negative-ion production on surfaces of insulating materials in low pressure hydrogen plasmas
International audienceIn this work negative-ion production on the surface of a sample negatively DC biased in a hydrogen plasma is studied. The negative ions created under the positive ion bombardment are accelerated towards the plasma, self-extracted and detected according to their energy and mass, by a mass spectrometer placed in front of the sample. The use of a pulsed bias allows applying a quasi-DC bias on insulating material during a short period of time and offers the possibility to extend the measurement method to nonconductive samples. The pulsed-bias tests were performed first with Highly Oriented Pyrolitic Graphite (HOPG), a conductive material, to demonstrate the feasibility of the method. By changing the pulsed-bias frequency it was possible to obtain HOPG material with different hydrogen surface coverages and hence different surface states leading to an increase of negative-ion production by up to 30-50% as compared to the continuous bias case. To establish a protocol for insulating materials, charge accumulation on the surface during the bias pulse and influence of the bias duration and frequency were explored using microcrystalline diamond (MCD) thin layers. By using a pulse short enough (10 µs) at 1 kHz frequency, it has been possible to measure negative-ions on MCD sample at a quasi-constant surface bias of 130 V, with only 1 V variation during the measurement. Negative-ion surface production on MCD has been studied in pulsed mode with surface temperature from room temperature to 800°C. It is shown that pulsing the bias and increasing the temperature allows limiting defect creation on MCD which is favorable for negative-ion production. Consequently, at 400°C the yield on MCD in pulsed mode is one order of magnitude higher than the yield on HOPG in continuous mode at room temperature