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Novel porous boron-doped diamond (BDD porous )-based materials have attracted lots of research interest due to their enhanced detection ability and biocompatibility, favouring them for use in neuroscience. This study reports on morphological, spectral, and electrochemical characterisation of three BDD porous electrodes of different thickness given by a number of deposited layers (2, 3 and 5). These were prepared using microwave plasma-enhanced chemical vapour deposition on SiO 2 nanofiber-based scaffolds. Further, the effect of number of layers and poly-l-lysine coating, commonly employed in neuron cultivation experiments, on sensing properties of the neurotransmitter dopamine in a pH 7.4 phosphate buffer media was investigated. The boron doping level of ∼2 × 10 21 atoms cm -3 and increased content of non-diamond (sp 2 ) carbon in electrodes with more layers was evaluated by Raman spectroscopy. Cyclic voltammetric experiments revealed reduced working potential windows (from 2.4 V to 2.2 V), higher double-layer capacitance values (from 405 μF cm -2 to 1060 μF cm -2 ), enhanced rates of electron transfer kinetics and larger effective surface areas (from 5.04 mm 2 to 7.72 mm 2 ), when the number of porous layers increases. For dopamine, a significant boost in analytical performance was recognized with increasing number of layers using square-wave voltammetry: the highest sensitivity of 574.1 μA μmol -1  L was achieved on a BDD porous electrode with five layers and dropped to 35.9 μA μmol -1  L when the number of layers decreased to two. Consequently, the lowest detection limit of 0.20 μmol L -1 was obtained on a BDD porous electrode with five layers. Moreover, on porous electrodes, enhanced selectivity for dopamine detection in the presence of ascorbic acid and uric acid was demonstrated. The application of poly-l-lysine coating on porous electrode surface resulted in a decrease in dopamine peak currents by 17% and 60% for modification times of 1 h and 15 h, respectively. Hence, both examined parameters, the number of deposited porous layers and the presence of poly-l-lysine coating, were proved to considerably affect the characteristics and performance of BDD porous electrodes., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Chemically inert and biocompatible boron-doped diamond (BDD) has been successfully used in neuroscience for sensitive neurochemicals sensing and/or as a growth substrate for neurons. In this study, several types of BDD differing in (i) fabrication route, i.e. conventional microwave plasma enhanced chemical vapour deposition (MW-PECVD) reactor vs. MW-PECVD with linear antenna delivery system, (ii) morphology, i.e. planar vs. porous BDD, and (iii) surface treatment, i.e. H-terminated (H-BDDs) vs. O-terminated (O-BDDs), were characterized from a morphological, structural, and electrochemical point of view. Further, planar and porous BDD-based electrodes were tested for sensing of dopamine in common biomimicking environments of pH 7.4, namely phosphate buffer (PB) and HEPES buffered saline (HBS). In HBS, potential windows are narrowed due to electrooxidation of its buffering component (i.e. HEPES), however, dopamine sensing in HBS is possible. H-BDDs (both planar and porous) outperformed O-BDDs as they provided clearer dopamine signals with higher peak currents. As expected, due to its enlarged surface area and increased sp 2 content, the highest sensitivity and lowest detection limits of 8 × 10 -8 mol L -1 and 6 × 10 -8 mol L -1 in PB and HBS media, respectively, were achieved by square-wave voltammetry on porous H-BDD., Competing Interests: Declaration of Competing Interest None., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Although Raman spectroscopy is a good tool for effective assessment of atomic boron concentration in diamond, determination of further physical properties using this non-destructive approach requires advancement in Raman analysis. In this work, we present an extended study of the Raman spectrum of boron-doped diamond, over a broad boron doping range and at increasing measurement temperature, based on the interaction between phonon and electronic Raman scattering effects. The presented analysis demonstrates the considerable contribution of electronic Raman scattering to the Raman spectrum and opens a practical route toward determination of additional boron-doped diamond properties, such as carrier concentration and carrier mobility. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Raman spectroscopy has been foreseen as a simple and non-destructive characterization method to determine the boron concentration in heavily boron-doped diamond with metallic conductivity. However, currently available empirical studies are not fully satisfactory for enabling accurate determination of the boron concentration in diamond. Here, we study Raman spectra of epitaxial boron-doped diamond as a function of the boron concentration and the excitation wavelength. The zone center phonon and the phonon density of state maximum (at ca. 1200 cm−1) lines are analyzed using a decoupled double Fano-function. This analysis method accurately describes the observed variation of the asymmetric parameters with atomic boron concentration and the photon excitation energy and enables the determination of the atomic boron concentration from the parameters of the examined Raman lines. Graphical abstract Unlabelled Image Highlights • Raman spectrum of highly boron-doped diamond are fitted between 1000 and 1500 cm-1 using a double Fano-function formalism • The dispersion of the asymmetric parameter of both Raman peaks with the boron concentration and the excitation wavelength is reported • Proportionality between the atomic boron concentration in diamond and the position and the width of the undisturbed Raman peaks is demonstrated [ABSTRACT FROM AUTHOR]

Lattice disorder, electronic Raman scattering, and Fano interaction effects are at the genesis of the Raman spectrum of heavily boron-doped diamond. However, no accurate unified description of this spectrum has been reported yet. In this work, we propose a novel analysis of the Raman spectrum of boron-doped diamond based on classical models of electronic Raman scattering and Fano effect. This new analysis shows that the Raman spectrum of boron-doped diamond results from the combination of electronic Raman scattering and its interaction, i.e. Fano effect, with the diamond phonon density of states and it confirms the 500 cm −1 and 1200 cm −1 bands originate from the phonon density of states. [ABSTRACT FROM AUTHOR]

Heavily boron doped nanocrystalline diamond films grown on glass substrates by the method of plasma-chemical deposition, were investigated using Raman spectroscopy. Analysis of the spectra showed both the phonon confinement effect in nanocrystalline grains and Fano interference effect due to the contribution of electron Raman scattering in heavily doped p-type diamond films. The increase of boron concentration led to decrease of the size of crystalline diamond grains. The films are semitransparent and have good conductivity, so that it can be used as transparent electrodes in giant-scale electronics and optoelectronics. [ABSTRACT FROM AUTHOR]

Characteristic Raman features of boron-doped diamond layers with metallic conduction are studied experimentally and discussed in comparison with an extensive selection of literature data. Despite evidence that the main Raman bands are mostly characteristic features of carbon atom vibration modes, their position is found to be proportional to boron concentration. While the origin of the Raman bands located at c.a. 500 cm −1 remains unclear, the band centred at c.a. 1200 cm −1 is attributed to a maximum of phonon density of states due to softening of the Raman wave vector conservation rule. The downshift and broadening of the diamond line are attributed, primarily, to the domain size effect caused by scattering on boron impurities, secondly to the Fano effect due to electronic Raman interaction, and finally to lattice expansion due to the boron doping. [ABSTRACT FROM AUTHOR]

Abstract: Boron doped diamond layers have been grown on (100) single crystal substrates in a wide range of boron concentration. The boron doped layers have been electrically and optically characterized. Boron doped layers with Hall mobility closes to natural diamond holes mobility have been obtained. The films morphology has been observed by scanning electron microscopy and their purity has been assessed by cathodoluminescence. Fourier Transform Photocurrent spectroscopy results show the evolution of the photo-ionization onset and the excited states as boron concentration in the films increases. [Copyright &y& Elsevier]

Boron-doped diamond layers have been grown by MW PECVD on substrates with a misorientation over the range of 0 to 90° relative to the (100) crystalline plane while keeping all other growth conditions constant. Deposited layers were characterized by scanning electron microscopy, atomic force microscopy, and Raman spectroscopy. The deposition rate, surface roughness, and boron incorporation vary according to the substrate misorientation. These results show the essential need for rigorous control of the substrate crystalline orientation in the synthesis of doped diamond for electronic applications. Thick, smooth, and free of surface defects boron-doped epitaxial diamond layers were obtained over a broad range of crystalline orientations at high growth rates and high boron incorporation efficiency. This work reports on the effect of the substrate crystalline orientation on the morphology, growth rate, and boron incorporation in epitaxial diamond layers deposited by plasma-enhanced chemical vapor deposition. [Display omitted] • Growth of boron-doped diamond on substrates with misorientation angle from 0 to 90° • Variation of the boron incorporation over two decades with the misorientation angle of the substrate • Growth of smooth and highly boron-doped epitaxial diamond layers on misoriented substrates over a large range of miscut angles [ABSTRACT FROM AUTHOR]

Electrical conductivity of a highly boron doped chemical vapor deposited diamond thin film has been studied at different temperatures under high electric field conditions. Current-voltage characteristics have been measured using pulsed technique to reduce thermal effects. Experimental results evidence deep impurity impact ionization avalanche in p-type diamond up to room temperature. [ABSTRACT FROM AUTHOR]

Electrical properties of epitaxial boron-doped diamond layers are studied at high electric fields in a wide range of boron concentration. Current-voltage characteristics co-planar concentric disk ring electrodes devices were measured using transmission line pulsed (TLP) characterization technique. Finite element method shows the electric field between test structures with co-planar plane parallel electrodes, used in previous studies, and concentric disk ring electrodes are comparable for inner ring electrode with a large diameter. The threshold electric field for the observed sudden increase of current, attributed to impurity impact ionization and/or self-heating, decreases from 130 kV·cm−1 to 70 kV·cm−1 with the increasing boron concentration in the epitaxial diamond layer. The measured quasi-static current grows exponentially with the electric field for energy dissipated in the devices limited below 2 μJ. Unlabelled Image • Breakdown field steadily decreases with the increasing boron concentration. • Current grows exponentially with the electrical field. • Devices with parallel and circular electrodes generate comparable electric field. [ABSTRACT FROM AUTHOR]

In this study complex characterization and comparison of as-grown and chemical-mechanical (CM) polished ultra-thin (≤500 nm) boron doped diamond (BDD) electrodes with various boron content (0.58–4.4 × 1021 cm−3, deposited with B/C 500–8000 ppm) was performed. Atomic force and scanning electron microscopy were used to compare morphological changes and confirm the reduction in roughness down to ≤2 nm. High-quality CM polishing enabled electron backscatter diffraction leading to the evaluation of grain size distribution (mean 0.3 μm) and preferred grain texture, {011}. X-ray photoelectron spectroscopy confirmed an increase in the B content on the surface of CM polished electrodes as a result of exposure of boron atoms incorporated into the bulk for highly doped BDD 4000 and BDD 8000 electrodes. Additionally, CM polished BDD electrodes are shown to possess uniform distribution of conductivity as proved by scanning electrochemical microscopy. This was reflected in faster heterogenous electron transfer kinetics for inner-sphere redox markers ([Fe(CN) 6 ]3–/4– and dopamine) and higher values of double layer capacitance in comparison with as-grown electrodes. These changes were more pronounced for low doped electrodes. Finally, the improvement in electrochemical characteristics was demonstrated by superior electroanalytical performance of CM polished BDD electrodes for dopamine detection. [Display omitted] • Chem-mechanical polishing of BDD with various [B] content. • Chem-mechanical polishing reveals bulk [B] content to the surface. • Chem-mechanical polishing leads to uniform distribution of electro-chemical surface activity. • Significant enhancement of HET kinetics recognized on chem-mechanical polished BDD electrodes. • Superior electroanalytical performance of chem-mechanical polished BDD electrodes for dopamine detection. [ABSTRACT FROM AUTHOR]

Boron doped diamond is a prospective material which can be used as a conductive and optically transparent thin-film electrode in a variety of optoelectronic applications. In this work, we present the results of the temperature resolved electrical conductivity, optical reflection, transmission and absorption of thin boron doped nanocrystalline diamond films grown by a microwave plasma enhanced chemical vapor deposition. Optical transmittance, reflectance and absorptance properties of layers were studied by a photo-thermal deflection spectroscopy analysis. Raman spectroscopy with various excitation wavelengths was employed for the analysis of nanocrystalline diamond layers. The measured position, shift and broadening of the characteristic boron doped diamond Raman lines were used for the determination of the boron concentration. Correlation between the results of the atomic boron concentration estimated via the Raman analysis and measured electrical conductivity values is presented. • Raman analysis has been used to determine the Boron concentration in the boron-doped nanocrystalline diamond films. • Electrical and optical properties of semitransparent and electrically conductive boron-doped nanocrystalline diamond layers. • Optical absorptance of the transparent conductive electrode measured by photothermal deflection spectroscopy. [ABSTRACT FROM AUTHOR]

Pseudo-vertical diodes on {113} oriented homoepitaxial boron-doped diamond were successfully fabricated using molybdenum as a metal for both the Schottky and ohmic contacts. After metal deposition, diodes were stabilized by annealing for 20 min at 300 °C and their I-V and C-V characteristics were measured at temperatures from 30 to 180 °C. Results show that Mo forms a very good and stable Schottky contact on {113} oriented homoepitaxial boron-doped diamond. At 180 °C, forward current densities higher than 1kA/cm2 are achieved, while the reverse current density stays unchanged at 10−8 A/cm2. The ideality factor of the diode I-V characteristic drops to 1.23 and the barrier height of the Schottky contact increases to 1.71 eV. This effect is attributed to inhomogeneity in the Schottky barrier. These characteristics are fully comparable with those of the best Schottky diodes fabricated on {100} oriented homoepitaxial boron-doped diamond. Results confirm that the use of {113} oriented homoepitaxial boron-doped diamond for the fabrication of high-temperature power devices is advantageous, as it enables high quality Schottky and ohmic contacts. [Display omitted] • First Mo/Au pseudo-vertical Schottky diodes on {113}-oriented BDD layers • Stable diode characteristic over wide range of temperatures • High rectification ratio of 1011 • Forward current density at 180 °C exceeds 1kA/cm2 at a forward voltage of 3 V [ABSTRACT FROM AUTHOR]

In this work, current multiplication at high electric field in epitaxial boron-doped diamond with high acceptor concentration is analyzed, including self-heating effect and impurity impact ionization. Quasi-static current-voltage (I-V) characteristics were measured using a transmission-line pulse setup with 100 ns pulse duration on samples with two Ohmic titanium/gold electrodes. Unambiguous exponential and super-exponential behaviors are observed in the I-V curves along with, in some cases, negative differential resistance. The self-heating effect is analyzed using transient interferometric mapping of the thermal energy distribution between electrodes with a ns time scale. Measured I-V characteristics are modeled by finite element method and by considering boron acceptor ionization due to self-heating effect and impurity impact ionization. Simulated I-V characteristics, in particular the appearance of the negative differential resistance region attributed to self-heating, are in good agreement with experimental data. Unlabelled Image • Super-linear and negative differential resistance behaviors observed in I-V characteristics • Thermal runaway and current filamentation revealed by optical measurements • Self-heating effect and impurity impact ionization were included in finite element simulations. • Simulated I-V curves convincingly match the experimental ones. [ABSTRACT FROM AUTHOR]