The paper presents nanocrystalline boron-doped diamond (B-NCD) film as a coating for optical fibres. Seeding and growth processes of thin diamond films on fused silica optical fibres have been investigated. B-NCD films were deposited using Microwave Plasma Assisted Chemical Vapour Deposition (MW PA CVD). Optical fibre pre-treatment by dip coating in detonation nanodiamond (DND) seeding media has been performed. For the coating purpose, the DND suspension in polyvinyl alcohol (PVA) was chosen. The grain size distribution of nanodiamond particles in seeding medium was kept at approx. 10-50 nm. The B-NCD surfaces were analysed using high-resolution scanning electron microscopy (HR-SEM). The molecular structure of diamond has been examined with micro-Raman Spectroscopy. The sp3/sp2 ratio was calculated using Raman spectra deconvolution method. Thickness, roughness and optical properties of the nanocrystalline diamond films in VIS-NIR wavelength range were investigated on reference samples using spectroscopic ellipsometry. The B-NCD films deposited on glass reference samples exhibit high refractive index (n=2.3 at lambda;=550 nm) and low extinction coefficient. Furthermore, cyclic voltammograms (CV) were recorded to determine the electrochemical window and reaction reversibility at the B-NCD fiber-based electrode. CV measurements in aqueous media consisting of 5 mM K3[Fe(CN)6] in 0.5 M Na2SO4 demonstrated a width of the electrochemical window up to 1.03 V and relatively fast kinetics expressed by a redox peak splitting below 500 mV. Moreover, thanks to high-n B-NCD overlay, the coated fibers can be also used for enhancing sensitivity of long-period gratings (LPGs) induced in the fiber. The LPG is capable for measuring variations in refractive index of surrounding liquid by tracing shift in resonance appearing in transmitted spectrum. Possible combined CV and LPG-based measurements are discussed in this work. Due to extraordinary properties of diamond, which include high chemical and mechanical resistance, such films are highly desired for optical sensing purposes.

Diamond is well known as an innovative solution in terms of low cost, miniaturization and sensitivity for electrochemical sensing. Moreover, boron doped diamond (BDD) excellent properties that include a wide potential window in aqueous media, high corrosion resistance, chemical inertness, biocompatibility and low background current, make diamond one of the most promising material for electrochemical sensing in real unprocessed samples. In order to increase the selectivity of these sensors, several studies have demonstrated the interest of the presence metallic nanoparticles such as Pt or Ir on BDD electrodes, to promote electro-catalytic activity and enhance the electrochemical performance. This leads to the possibility to detect new species and namely derived products from enzymatic reactions such as acetylcholine oxidation. Here we have used this approach on a multiplexed system of several electrochemical sensors in order to fabricate an electronic tongue based on multiple metallic groups on BDD electrodes. From this approach, the simultaneous detection of analytes in a complex medium by an array of BDD electrodes covered with different kinds of metallic nanoparticles provides a unique finger print signature for each analyte, increasing the specificity and the selectivity of the sensor.
In this communication we will describe the process enabling the deposition of metallic nanoparticles: the approach used two steps: first, a thin film of a few nanometres was deposited using physical vapour deposition, and then this layer was submitted to an hydrogen plasma treatment, to de-wet the metallic layer while the diamond surface remains hydrogenated. Conditions were optimized to obtain nanoparticles with a subsequent narrow size distribution (20 +/- 3 nm) and an homogeneous particle density. Nanoparticles deposited by this method exhibit a very good stability in term of electro-activity and adhesion on BDD, even after several hundreds of current pulses up to 50mA.s^-1. Here we present the use of this innovative electronic tongue for specific detection of several chemicals i.e. Paraoxon and imidacloprid, known toxic water pollutants for humans.

Boron Doped Nanocrystalline Diamond (B-NCD) is known as a remarkable material for the fabrication of neural interfaces, taking advantage in particular of its good biocompatibility, electrochemical properties, and stability. Over the last years, in collaboration with electrophysiologists and biologists, such material was structured in various ways to design diamond devices, including MicroElectrode Arrays (MEAs) enabling to probe the neuronal activity distributed over large populations of either neurons or embryonic organs. Such developments were conducted within the frame of the Neurocare FP7 EU funded project, gathering technologists, electrophysiologists, biologists, and neurophysiologists. Specific MEAs were built such as neural prostheses or implants in order to compensate function losses due to lesions or degeneration of part of neural tissues like the retina.
However, despite remarkable properties in vivo and stimulating and recording properties very close to that of platinum, diamond exhibits a rather low double layer capacitance and a high interfacial impedance thus precluding its use for the fabrication of novel microelectrodes that go beyond the state of the art achievable with other materials (SIROF, Black Pt, Pedot etc).
This motivated the development of novel forms of diamond coatings based on highly porous and conductive carbonated materials to obtain highly porous diamond electrodes. The approach relies on the ability to grow diamond at low temperatures on 3D shape porous materials using electrostatic grafting of nanodiamonds as a seeding layer. The approach led to the fabrication a new material where a thick porous polypyrrole layer is uniformly coated with diamond. This material, now named SPDia^TM, exhibits a capacitance value increased up to a factor 800 with respect to planar diamond, as well as very low electrochemical interfacial impedances.
MEAs fabricated using SPDia^TM exhbit electrochemical performances matching those of the most advanced materials such as PEDOT-CNT, Iridium Oxide or porous Platinum, and further exhibit the remarkable biocompatibility of diamond.
Although not directly conducted within the NEUROCARE project, the authors would like to strongly acknowledge the EU Commission for its support under the GA FP7-NMP-280433, as well as all partners of the project from whom this work would not have been made feasible, with special thanks to L. Rousseau and G. Lissorgues from the ESIEE group and S. Picaud from the Vision Institute in Paris.

Synthetic diamond is a material with vast potential in a variety of fields, ranging from a bio-compatible substrate for biological devices to high-power electronics and solar-power devices. Diamond is routinely grown by chemical vapour deposition (CVD), and p-type semiconductivity can be easily achieved using diborane (Bshy;₂H₆) in the precursor gases of this process. However, despite several candidate dopants, true n-type semiconductivity has never been successfully achieved, and atomic-scale characterisation is essential to this goal.
Atom Probe Tomography (APT) is a perfect tool to characterise the distribution of dopants within diamond films. APT is based upon the controlled evaporation of individual ions from a very sharp needle-shaped specimen, projecting them onto a position-sensitive time-of flight detector. From the resulting data, a three-dimensional atomistic reconstruction of the tip, incorporating millions of these ions, is computer generated with highly accurate spatial resolution and elemental composition. Recent instrument advances and in particular the advent of the laser-assisted local electrode atom probe (LEAP) has opened the technique up to the study of semiconductors and even insulating materials. Previous investigations of diamond-based materials using atom probe tomography are extremely limited, but a recent successful study utilising it to date meteoritic nanodiamond [1] highlights its potential. However, as yet there have been no investigations into synthetic or doped diamond using the latest generation of laser-assisted atom probes.
This talk will discuss the use of APT to map the behaviour and location of dopant atoms in CVD diamond films. One key advantage of the CVD approach is that diamond films can be grown directly onto commercially available presharpened silicon microtips. This eliminates the need for the Focused Ion Beam (FIB) liftout procedure usually used to prepare atom probe needles, which is unsuitable for diamond due to its uneven milling behaviour and evaporation mismatch with weld materials. We have successfully used this approach to demonstrate that boron is homogenous within the grain of residually boron-doped nanocrystalline diamond films. This talk will go on to look in more detail at the preparation methods and analysis parameters optimal for imaging diamond using APT, the effect of different grain sizes and doping levels of boron-doped films, as well as looking at the various candidates for n-type doping of diamond - primarily phosphorus, lithium, and nitrogen.
[1]B Lewis et al, Meteoritic nanodiamond analysis by atom-probe tomography, 43^rd Lunar and Planetary Science Conference (2012)

In the past decade, tremendous improvements in the crystalline quality and purity of Chemically Vapour Deposited (CVD) diamond films have been achieved. Millimetre-thick CVD plates with an area close to 1 cmsup2; have now been made commercially available by several suppliers, opening the way to new applications in optics and electronics thanks to the outstanding properties of single crystal diamond. Nevertheless reducing extended defects in synthetic diamond still remains an important challenge. For example, dislocations affect current leakage in power devices, generate background fluorescence, or induce strain and unwanted birefringence of optical components. To achieve an optimal performance new strategies and technologies aiming at reducing dislocation densities are highly required.
In that context, analysing and identifying the nature and origin of dislocations in diamond can rely on a combination of several techniques. Dislocations can be revealed and counted using selective etching with H₂/O₂ plasma. By measuring the strain field surrounding a dislocation with Birefringence Microscopy (BM), important information can be obtained on the Burgers vector of the dislocation. Cathodoluminescence (CL) can also image the propagation direction of dislocations since they behave as efficient recombination centres for excitons. Finally, Transmission Electron Microscopy (TEM) allows a full identification of the type and Burgers vector of a dislocation. However, it requires heavy equipment and the preparation of a thin lamella of material.
In this work, dislocations produced in a thick CVD diamond crystal are analysed using a combination of plasma etching, BM, CL and TEM. It was found that dislocations are mostly of the mixed 45° or pure edge type. Each one leads to a recognisable etch-pit pattern. The advantages of each technique are discussed in order to get a better understanding of the formation of these defects in the synthetic material towards developing higher performance devices.

Bulk boron doped single crystal diamonds can be used as electric and thermal conductive substrates for wide variety of electronic devices. Detailed experimental data on electrical and thermal properties is required to model and design diamond based devices. Electrical transport properties of such crystals were reported in [1].
In this work we studied thermal conductivity of pure IIa and boron-doped IIb single crystal diamonds grown by the temperature gradient method under high pressure and high temperature (HPHT). The boron content was <10¹⁶ and ~10¹⁹ cm^-3. Thermal conductivity measurements were carried out using Quantum Design PPMS by steady-state method in temperature range from 400 to 20 K on specially cut thin samples.
The thermal conductivity data has the accuracy less than 6% in the range 20-400 K.
The data was interpreted and fitted using the Callaway model. We considered phonon-phonon scattering, boundary scattering, scattering on point defects (¹³C isotopes and substitutional boron atoms) and extended defects (dislocations, etc.).
At low temperatures the thermal conductivity of boron-doped IIb diamond was found to be 2-4 times less than the thermal conductivity of pure IIa diamond. On the other side at high temperatures (>300 K) the difference is less than 30%. The decrease of thermal conductivity for boron-doped IIb diamond at T > 140 K is caused mostly by extended defects. In the operational range of diamond electronic devices (>300 K) the decrease of thermal conductivity of boron-doped IIb diamond should be taken into account, but it is unlikely that it can have critical influence on their performance.
[1] V.S. Bormashov, et al., Electrical properties of the high quality boron-doped synthetic single-crystal diamonds grown by the temperature gradient method, Diam. Relat. Mater. 35 (2013) 19-23.

Nanodiamond (ND) electronic and optical properties may be tuned by surface termination, which is important for their usage in nano-chemical, sensing or energy conversion devices. Atomic termination is commonly achieved by a plasma treatment in the specific gas atmosphere. Recent experiments indicate that thermal and plasma treatments have a more complex effect on NDs compared to bulk diamond [Petit et al., Phys Rev. B 84, 233407 (2011)]. This can be attributed to nanoscale dimensions and commonly present amorphous carbon shell of the NDs, be they of detonation or HPHT origin. The amorphous carbon phase significantly influences electronic properties of detonation NDs as recently observed by surface potential measurements (KPFM) in correlation with infrared spectroscopy (FTIR) [Kromka et al., Phys.Stat.Sol. (b) 2015, in press]. In order to better understand the influence of surface treatment and surface condition on NDs electronic properties we performed local electrical conductivity measurements on individual and aggregated NDs by atomic force microscopy (AFM).
The detonation and HPHT NDs are characterized in the as-received state (i.e. after wet chemical cleaning), after plasma treatment in hydrogen, and after thermal annealing in air. Gold layers sputtered on n-doped silicon are used as electrically conductive, non-oxidizing substrates. NDs are deposited by immersing the substrates in the appropriate ND aqueous solution for 5 s. The samples are let dry in air and prior measurement they are heated to 180°C for 30 min (hot plate) to evaporate adhered moisture. AFM is operated in the PeakForce conductivity regime (PF-TUNA) which probes the electric current (in the range of < 10 pA) flowing between the substrate (biased up to +4 V) and the AFM tip during controlled cantilever approach-retract movements at low frequency (1 kHz). The differences in NDs conductivities are well correlated with FTIR and KPFM data. The influence of plasma treatment time, air moisture, carbon shell, contact barrier as well as actual diamond surface termination on the electrical conductivity of NDs will be discussed with view to their potential uses in sensors or energy conversion devices.

With their outstanding properties and ability to withstand harsh conditions, nanocrystalline diamond (NCD) membranes are a promising candidate for future use as sensitive pressure detectors [1]. The transparency of glass allows a straightforward fabrication procedure on this substrate material. Here we&’ll discuss the fabrication of ultra-thin NCD membranes on different types of glass and the study of their piezoresistive properties when bulged under varying differential pressure. To this end, the membranes are positioned in the middle of a Hall bar structure, enabling the continuous probing of their electrical properties.
It will be shown that the underlying substrate plays an important role in the final pressure sensitivity of the membrane on top. This is primarily due to the amount of stress created in the film during the diamond growth process, leading to wrinkle formation. Heavily boron doped NCD membranes show a straight dependence of the sensor sensitivity on the type of glass substrate, directly observable by the amount of wrinkles in the membrane itself. The difference in thermal expansion coefficient between the glass types and the NCD film is thought to be responsible for this difference in stress, leading to an increase in sensitivity of 5 3% for membranes on Corning Eagle 2000 glass compared to those on Schott AF45 glass.
Furthermore, piezoresistive effect measurements on undoped H-termined surface conducting NCD membranes are discussed [2]. These measurements reveal additional information on the complex transport mechanisms in this granular material and encourage further research on the piezoresistive properties of diamond.
References
[1] S.D. Janssens, S. Drijkoningen, K. Haenen, Applied Physics Letters 104/7 (2014), 073107.
[2] S.D. Janssens, S. Drijkoningen, K. Haenen, Applied Physics Letters 105/11 (2014), 101601.
Acknowledgements
SDJ is a Postdoctoral Fellow of the Japan Society for the Promotion of Science (JSPS).

The growing interest for high resolution X-Ray imaging in medical and industrial applications leads to increasing developments in the field of micro-focus transmission X-Ray tubes. In order to improve next generation devices, the subsequent increase of the power density and predicted instability of the emission currents must be addressed. We report here of the realization of innovative diamond windows where an integrated diamond detector is embedded in order to measure in real time the dose emitted by the X-ray tube without disturbing its operation. This ultimately leads to the possible fine control of the current instabilities via feedback loop control.
To understand and predict the mechanical and thermal specifications of such smart-windows, we modelled the physical parameters of the system. First the mechanical behaviour has been studied in order to downsize accurately the window. Then, a thermal analytical model has been developed to predict the temperature distribution within diamond windows under operating conditions and to check the mechanical downsizing. Finally the detection performances were modelled using Monte-Carlo simulations in order to predict the operating specifications of the devices as a function of the generated photocurrents.
Experimentally, several set-ups have been designed and used to characterize prototype devices. First, diamond smart-windows of 1 cm² and 100 µm thick were grown using a homemade MPECVD reactor. Large diamond grains improve the heat spreading in the target and a smooth surface is required for its deposition. Hence films with a controlled (100) texture have been synthesized. A combined laser interferometric and scattered intensity set-up has been developed to optimize the diamond microstructure. Synthetized diamond windows prototypes have further been brazed on metallic rings in order to perform fatigue tests for up to 10⁴ cycles under vacuum differential pressures. Eventually, the detection performances of such diamond smart-windows have been qualified under X-Ray exposure. A homemade EBIC set-up has