Surface-induced charge state conversion of nitrogen-vacancy defects in nanodiamonds

We present a study of the charge state conversion of single nitrogen-vacancy (NV) defects hosted in nanodiamonds (NDs). We first show that the proportion of negatively-charged NV$^{-}$ defects, with respect to its neutral counterpart NV$^{0}$, decreases with the size of the ND. We then propose a simple model based on a layer of electron traps located at the ND surface which is in good agreement with the recorded statistics. By using thermal oxidation to remove the shell of amorphous carbon around the NDs, we demonstrate a significant increase of the proportion of NV$^{-}$ defects in 10-nm NDs. These results are invaluable for further understanding, control and use of the unique properties of negatively-charged NV defects in diamondComment: 6 pages, 4 figure

Boron Doped Diamond Electrodes for Direct Measurement in Biological Fluids: An In Situ Regeneration Approach

International audienceBoron doped diamond (BDD) electrodes are extremely promising in the field of biomedical applications as they exhibit a unique combination of properties. Despite these advantages, BDD electrodes are prone to fouling when used in biological fluids (urine, blood plasma), and synthetic fluids. We propose a electrochemical (EC) treatment where a train of short cathodic and/or anodic pulses are applied to clean fouled electrodes. This technique can be used to retrieve the lost reactivity, characterized by electron transfer rate k0 of the boron doped diamond electrodes, thereby enhancing their reusability over long period of measurements without degradation of the signal, thus significantly extending the field of monitoring and surveying applications. The technique does not require the use of a specific medium and thus can be directly performed in the probed fluid. Although an aqueous electrolyte containing non-electroactive species is preferred for EC activation, it can also be done in biological fluids such as blood, urine etc, thereby opening the field for $in-vivo$ analysis. Through Electrochemical impedance spectroscopy (EIS) it was observed that the k$_0$ value was increased up to 0.1 cm s$^{−1}$ after the activation process. This technique improves the sensitivity, reproducibility and lifetime of the electrodes to a considerable extent

Development of Diamond Tracking Detectors for High Luminosity Experiments at LHC

During 2006 detectors based on new polycrystalline CVD (pCVD) material were produced as candidates for use in LHC experiments. The first full size diamond pixel module with ATLAS specifications using a $2 \times 6$ cm$^2$ pCVD sample was characterized in the 2006 CERN test beam. Radiation damage studies performed outside of CERN corroborate the radiation hardness of this material. Radiation hardness studies at CERN using the highest quality diamond were deferred until 2007 due to the PS magnet problem. ATLAS, CMS, ALICE and LHCb are planning to use diamond for their beam conditions monitoring systems. Construction of the BCM system for ATLAS was completed in 2006 and the BCM modules were characterized in 2006 CERN test beams. Similar devices are under construction for the CMS, ALICE and LHCb experiments. Single-crystal CVD (scCVD) samples were produced and made available to RD42 institutes. The first scCVD diamond pixel device was constructed and tested in the 2006 CERN test beams. In this report we present the progress and work done by the RD42 collaboration on the development of CVD diamond material for radiation detectors

Proton irradiation of CVD diamond detectors for high-luminosity experiments at the LHC

CVD diamond shows promising properties for use as a position sensitive detector for experiments in the highest radiation areas at the Large Hadron Collider. In order to study the radiation hardn ess of diamond we exposed CVD diamond detector samples to 24~GeV/$c$ and 500~MeV protons up to a fluence of $5\times 10^{15}~p/{\rm cm^2}$. We measured the charge collection distance, the ave rage distance electron hole pairs move apart in an external electric field, and leakage currents before, during, and after irradiation. The charge collection distance remains unchanged up to $1\ times 10^{15}~p/{\rm cm^2}$ and decreases by $\approx$40~\% at $5\times 10^{15}~p/{\rm cm^2}$. Leakage currents of diamond samples were below 1~pA before and after irradiation. The particle indu ced currents during irradiation correlate well with the proton flux. In contrast to diamond, a silicon diode, which was irradiated for comparison, shows the known large increase in leakage curren t. We conclude that CVD diamond detectors are radiation hard to 24~GeV/$c$ and 500~MeV protons up to at least $1\times 10^{15}~p/{\rm cm^2}$ without signal loss

Enhanced Conformational Sampling using Replica Exchange with Collective-Variable Tempering

The computational study of conformational transitions in RNA and proteins with atomistic molecular dynamics often requires suitable enhanced sampling techniques. We here introduce a novel method where concurrent metadynamics are integrated in a Hamiltonian replica-exchange scheme. The ladder of replicas is built with different strength of the bias potential exploiting the tunability of well-tempered metadynamics. Using this method, free-energy barriers of individual collective variables are significantly reduced compared with simple force-field scaling. The introduced methodology is flexible and allows adaptive bias potentials to be self-consistently constructed for a large number of simple collective variables, such as distances and dihedral angles. The method is tested on alanine dipeptide and applied to the difficult problem of conformational sampling in a tetranucleotide

Micro-strip sensors based on CVD Diamond

In this article we present the performance of recent chemical vapour deposition (CVD) diamond micro-strip sensors in beam tests. In addition we present the first comparison of a CVD diamond micro-strip sensor before and after proton irradiation