Boron-doped Nanocrystalline Diamond Research Articles

Towards Alpha Radiation Detection in Aqueous Solution: VLSI Technology Development for Diamond-Silicon Hybrid Sensors

ABSTRACTIn the presented work, we have developed VLSI technology processes for new prototype sensors based on the synthesis of boron doped nanocrystalline diamond (B-NCD) and silicon based commercial detectors. The process is based on commercial passivated implanted planar silicon (PIPS) devices of PD450 and CAM450 types (CANBERRA). A layer of B-NCD of several hundred nanometers thickness and boron concentration up to 1021 atoms/cm3 is grown on the SiOx passivation layer in an ellipsoidal plasma enhanced chemical vapor deposition (PECVD) reactor at temperatures from 520-750°C, in hydrogen atmosphere. . The diamond electrode is dry chemically structured and aluminum electrodes are realized before mounting in a three-fold housing for measurements in aqueous solution. The prototype sensors show an alpha spectroscopy resolution of 100 keV for 241Am electroprecipitated from liquid solution.

Visible-light sensitization of boron-doped nanocrystalline diamond through non-covalent surface modification.

A novel simple and versatile synthetic strategy is developed for the surface modification of boron-doped diamond. In a two-step procedure, polyethyleneimine is adsorbed on the hydrogenated diamond surface and subsequently modified with a model light-harvesting donor-π-bridge-acceptor molecule (coded P1). The sensitized diamond exhibits stable cathodic photocurrents under visible-light illumination in aqueous electrolyte solution with dimethylviologen serving as an electron mediator. In spite of the simplicity of the surface sensitization protocol, the photoelectrochemical performance is similar to or better than that of other sensitized diamond electrodes which were reported in previous studies (2008-2014).

Investigation of Boron Doped Nanocrystalline Diamond Films Grown on Porous Silicon Substrate under Different Doping Concentrations

The production and characterization of porous silicon (PS) samples were studied as well as their use as substrates to grow boron doped nanocrystalline diamond (NCD) films. PS represents a suitable material for diamond growth due to its large number of nucleation sites and surface area, becoming an excellent material for porous electrodes. NCD films were grown by chemical vapor deposition (CVD) technique by balancing H2/CH4/Ar gas mixture, at two different boron levels. Doping was conducted by an additional hydrogen line passing through a bubbler containing B2O3 dissolved in methanol. Two ratios of boron/carbon were used of 2000 and 20000 ppm in the bubbler solution. Scanning electron microscopy, Raman spectroscopy and X-ray diffraction were used to characterize the films as well as the PS substrate. Results showed that it is possible to obtain NCD films on PS substrate with good quality at different doping levels.

Boron-Doped Ultra/Nanocrystalline Diamond Films Obtained with Different Growth Times and Boron Doping Levels

In this work, the achievement and characterization of boron-doped nanocrystalline diamond films is presented. A series of experiments varying boron doping levels from 2,000 to 30,000 ppm and film growth times during 6, 10 and 16 h were performed. These films were analyzed by Scanning Electron Microscoy (SEM), Atomic Force Microscopy (AFM), Raman spectroscopy and Cyclic Voltammetry (CV) measurements. The results showed that the films presented two morphologies: ultra and nanocrystalline diamond. From Raman spectroscopy, the doping level increase for all the films, independent of growth time, increased the boron acceptor number and it was confirmed by Mott-Schottky plot (MSP). Electrochemical response showed the influence of boron content in the work potential window, mainly for films grown during 6 h. However, the reversibility was almost independent on the boron content for samples grown during 16 h.

Evaluation of Histamine Imprinted Polypyrrole Deposited on Boron Doped Nanocrystalline Diamond

AbstractThis study describes the evaluation of histamine imprinted polypyrrole deposited on boron doped nanocrystalline diamond (NCD). Boron doped oxygen terminated NCD (B : NCD) was used as a conducting substrate for the design of here reported electrochemical sensor. Some peculiarities of B : NCD were evaluated and oxidation kinetics of both NCD and B : NCD was investigated. Both the NCD and B : NCD were modified by molecularly imprinted polypyrrole and not‐imprinted polypyrrole. Histamine was used as a template for molecular imprinting of polypyrrole. Electrochemical impedance spectroscopy was applied for the evaluation of formed MIP and NIP layers.

Thermoelectric transport properties of boron-doped nanocrystalline diamond foils

Natural diamond is known for its outstanding thermal conductivity and electrical insulation. However, synthetic production allows for doping and tailoring microstructural and transport properties. Despite some motivation in the literature and the ongoing search for abundant and non-toxic thermoelectric materials, the first experimental study on a set of eight substrate-free boron-doped nanocrystalline diamond foils is presented herein. All transport coefficients were determined in the same direction within the same foils over a broad temperature range up to 900°C. It is found that nanostructuring reduces the thermal conductivity by two orders of magnitude, but the mobility decreases significantly to around 1cm2V−1s−1, too. Although degenerate transport can be concluded from the temperature dependence of the Seebeck coefficient, charge carriers notably scatter at grain boundaries where sp2-carbon modifications and amorphous boron-rich phases form during synthesis. A detailed analysis of doping efficiency yields an acceptor fraction of only 8–18at%, meaning that during synthesis excess boron thermodynamically prefers electrically inactive sites. Decent power factors above 10−4Wm−1K−2 at 900°C are found despite the low mobility, and a Jonker-type analysis grants a deeper insight into this issue. Together with the high thermal conductivity, the thermoelectric figure of merit zT does not exceed 0.01 at 900°C.

Boron Doped Nanocrystalline Diamond Grown on Reticulated Vitreous Carbon: Morphological, Structural, and Electrochemical Characterizations

Reticulated vitreous carbon (RVC) is a macroporous material with high surface area, rigid structure, low resistance to fluid flow and high thermal and electrical conductivities. RVC has a wide range of applications as porous electrodes, high temperature insulation, filters, storage batteries, among others. Composites formed from diamond grown on sp2 bonded carbonaceous materials have already been studied, but there are still few publications about the electrochemical properties of this material. Then, the study of new hybrid nanomaterials is very important for understanding and promoting new technologies. In this work, boron-doped nanocrystalline diamond (BDND) films were deposited on RVC heat treated until 1000 °C and 1700 °C in order to evaluate the influence of different structural organization indexes of RVC on the nanocrystalline diamond grains formation as well as on their electrochemical performance. RVC was processed using poly(furfuryl) alcohol and polyurethane foams with 70 ppi (pores per inch) as mold. RVC substrates surfaces were prepared using seeding treatment in which samples are dipped in a 10 wt% solution of Poly diallyldimethylammonium chloride (PDDA) during 30 min followed by immersion in a nanodiamond (4nm) seeding dispersion for 10 min. The seeding step is necessary to improve diamond growth on carbon fiber in order to keep the surface carbon in sp3 configuration dominant over sp2 bond etching during diamond film growth. BDND films were grown on RVC heat treated until 1000 °C and 1700 °C using a hot-filament chemical vapor deposition (HFCVD) reactor. The boron doping was performed by dissolving B2O3 in methanol in a bubbler attached to the reactor. The solution was prepared with a concentration of B2O3 dissolved in CH3OH that correspond to B/C ratio of 30000 ppm. Hydrogen gas was used as a carrier with a constant flow of 30 sccm. The composites were evaluated by Scanning Electron Microscopy (SEM), Raman spectroscopy and cyclic voltammetry. Raman spectra and SEM images confirmed the BDND films achievement showing the RVC completely covered by a diamond coating. The electrochemical measurements were made by using Autolab PGSTAT 302 equipment with a three-electrode cell. The BDND/RVC composites obtained with different RVC heat treatment temperature (HTT), were used as working electrode. A platinum coil wire served as the counter electrode and Ag/AgCl was used as the reference electrode. The voltammetric curves (VC) were taken in H2SO4 0.5 mol.L-1 and showed a standard wide potential window as expected for BDND electrodes. In order to characterize the electrochemical kinetic we have applied CV using the redox couple of Fe(CN)6 3-/4- with different scan rates. This redox system includes reactions that depend on the specific interactions with the surface electrode. Besides, the electrode kinetics for this kind of redox couple tends to be more sensitive to the surface functionalities on sp2-bonded carbon electrodes. The BDND grown on RVC with higher HTT demonstrated the fast kinetics attributed to the better conductivity of such substrate.

Optimization of Actinides Trace Precipitation on Diamond/Si PIN Sensor for Alpha-Spectrometry in Aqueous Solution

We report here on a new approach for the detection and identification of actinides ( 239 Pu, 241 Am, 244 Cm, etc). This approach is based on the use of a novel device consisting of a boron doped nanocrystalline diamond film deposited onto a silicon PIN diode alpha particle sensor. The actinides concentration is probed in situ in the measuring solution using a method based on electro-precipitation that can be carried out via the use of a doped diamond electrode. The device allows probing directly both alpha-particles activity and energy in liquid solutions. In this work, we address the optimization of the actinides electro-precipitation step onto the sensor. The approach is based on fine tuning the pH of the electrolyte, the nature of the supporting electrolytes (Na 2 SO 4 or NaNO 3 ), the electrochemical cell geometry, the current density value, the precipitation duration as well as the sensor surface area. The deposition efficiency was significantly improved with values reaching for instance up to 81.5% in the case of electro-precipitation of 5.96 Bq 241 Am on the sensor. The diamond/silicon sensor can be reused after measurement by performing a fast decontamination step at high yields ≥99%, where the 241 Am electro-precipitated layer is quickly removed by applying an anodic current (+2 mA · cm -2 for 10 minutes) to the boron doped nanocrystalline diamond electrode in aqueous solution. This study demonstrated that alpha-particle spectroscopic measurements could be made feasible for the first time in aqueous solutions after an electrochemical deposition process, with theoretical detections thresholds as low as 0.24 Bq · L -1 . We believe that this approach can be of very high interest for alpha-particle spectroscopy in liquids for actinides trace detection.

Impact of differently modified nanocrystalline diamond on the growth of neuroblastoma cells

The aim of this study was to assess the impact of nanocrystalline diamond (NCD) thin coatings on neural cell adhesion and proliferation. NCD was fabricated on fused silica substrates by microwave plasma chemical vapor deposition (MPCVD) method. Different surface terminations were performed through exposure to reactive hydrogen and by UV induced oxidation during ozone treatment. Boron doped NCD coatings were also prepared and investigated. NCD surface wettability was determined by contact angle measurement. To assess biocompatibility of the NCD coatings, the neuroblastoma SH-SY5Y cell line was used. Cells were plated directly onto diamond surfaces and cultured in medium with or without fetal bovine serum (FBS), in order to evaluate the ability of cells to adhere and to proliferate. The obtained results showed that these cells adhered and proliferated better on NCD surfaces than on the bare fused silica. The cell proliferation on NCD in medium with and without FBS after 48h from plating was on average, respectively, 20 and 58% higher than that on fused silica, irrespective of NCD surface modification. Our results showed that the hydrogenated, oxygenated and boron-doped NCD coatings can be used for biomedical purposes, especially where good optical transparency is required.

Contactless photoconductance study on undoped and doped nanocrystalline diamond films.

Hydrogen and oxygen surface-terminated nanocrystalline diamond (NCD) films are studied by the contactless time-resolved microwave conductivity (TRMC) technique and X-ray photoelectron spectroscopy (XPS). The optoelectronic properties of undoped NCD films are strongly affected by the type of surface termination. Upon changing the surface termination from oxygen to hydrogen, the TRMC signal rises dramatically. For an estimated quantum yield of 1 for sub-bandgap optical excitation the hole mobility of the hydrogen-terminated undoped NCD was found to be ∼0.27 cm(2)/(V s) with a lifetime exceeding 1 μs. Assuming a similar mobility for the oxygen-terminated undoped NCD a lifetime of ∼100 ps was derived. Analysis of the valence band spectra obtained by XPS suggests that upon oxidation of undoped NCD the surface Fermi level shifts (toward an increased work function). This shift originates from the size and direction of the electronic dipole moment of the surface atoms, and leads to different types of band bending at the diamond/air interface in the presence of a water film. In the case of boron-doped NCD no shift of the work function is observed, which can be rationalized by pinning of the Fermi level. This is confirmed by TRMC results of boron-doped NCD, which show no dependency on the surface termination. We suggest that photoexcited electrons in boron-doped NCD occupy nonionized boron dopants, leaving relatively long-lived mobile holes in the valence band.

Nanocrystalline diamond on Si solar cells for direct photoelectrochemical water splitting

This article presents a study of a boron‐doped nanocrystalline diamond (B‐NCD) and crystalline silicon solar cell (c‐Si SC) heterostructure designed for direct photoelectrochemical water splitting application. A system is proposed which generates voltages sufficient for water‐splitting via light absorption by solar cells. The rear side (photo‐anode) of the c‐Si solar cell was shielded with the B‐NCD layer intended to serve as a protective coating to eliminate corrosion of the Si and operate as a p‐type conductive electrode suited for water decomposition. Information on the efficiency of the c‐Si/B‐NCD heterostructure and the distribution of the electric potential has been gained through investigation of minority carrier recombination mapping. The results of the B‐NCD layer characterization by Raman spectroscopy, AFM, SEM and optical reflection measurements are presented. It is demonstrated that inclusion of a boron (p+) diffusion layer into a c‐Si solar cell structure prevents lifetime (LT) degradation caused by the B‐NCD deposition process. In addition it is shown that the B‐NCD deposition temperature has a substantial effect on the properties of c‐Si solar cell.

Heterogeneous distribution of exocytotic microdomains in adrenal chromaffin cells resolved by high-density diamond ultra-microelectrode arrays.

Here we describe the ability of a high-density diamond microelectrode array targeted to resolve multi-site detection of fast exocytotic events from single cells. The array consists of nine boron-doped nanocrystalline diamond ultra-microelectrodes (9-Ch NCD-UMEA) radially distributed within a circular area of the dimensions of a single cell. The device can be operated in voltammetric or chronoamperometric configuration. Sensitivity to catecholamines, tested by dose-response calibrations, set the lowest detectable concentration of adrenaline to ∼5 μm. Catecholamine release from bovine or mouse chromaffin cells could be triggered by electrical stimulation or external KCl-enriched solutions. Spikes detected from the cell apex using carbon fibre microelectrodes showed an excellent correspondence with events measured at the bottom of the cell by the 9-Ch NCD-UMEA, confirming the ability of the array to resolve single quantal secretory events. Subcellular localization of exocytosis was provided by assigning each quantal event to one of the nine channels based on its location. The resulting mapping highlights the heterogeneous distribution of secretory activity in cell microdomains of 12-27 μm2. In bovine chromaffin cells, secretion was highly heterogeneous with zones of high and medium activity in 54% of the cell surface and zones of low or no activity in the remainder. The 'non-active' ('silent') zones covered 24% of the total and persisted for 6-8 min, indicating stable location. The 9-Ch NCD-UMEA therefore appears suitable for investigating the microdomain organization of neurosecretion with high spatial resolution.

Functionalization of Boron-Doped Nanocrystalline Diamond with N3 Dye Molecules

N3 dye molecules [cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II)] are covalently attached to boron-doped nanocrystalline diamond (B:NCD) thin films through a combination of coupling chemistries, i.e., diazonium, Suzuki, and EDC-NHS. X-ray and ultraviolet photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy are used to verify the covalent bonding of the dye on the B:NCD surface (compared to a hydrogen-terminated reference). The spectroscopic results confirm the presence of a dense N3 chromophore layer, and the positions of the frontier orbitals of the dye relative to the band edge of the B:NCD thin film are inferred as well. Proof-of-concept photoelectrochemical measurements show a strong increase in the photocurrent compared to non-dye-functionalized B:NCD films. This study opens up the possibility of applying N3-sensitized B:NCD thin films as hole conductors in dye-sensitized solar cells.

Lead detection using micro/nanocrystalline boron-doped diamond by square-wave anodic stripping voltammetry

Monitoring heavy metal ion levels in water is essential for human health and safety. Electroanalytical techniques have presented important features to detect toxic trace heavy metals in the environment due to their high sensitivity associated with their easy operational procedures. Square-wave voltammetry is a powerful electrochemical technique that may be applied to both electrokinetic and analytical measurements, and the analysis of the characteristic parameters of this technique also enables the mechanism and kinetic evaluation of the electrochemical process under study. In this work, we present a complete optimized study on the heavy metal detection using diamond electrodes. It was analyzed the influence of the morphology characteristics as well as the doping level on micro/nanocrystalline boron-doped diamond films by means of square-wave anodic stripping voltammetry (SWASV) technique. The SWASV parameters were optimized for all films, considering that their kinetic response is dependent on the morphology and/or doping level. The films presented reversible results for the Lead [Pb (II)] system studied. The Pb (II) analysis was performed in ammonium acetate buffer at pH 4.5, varying the lead concentration in the range from 1 to 10μgL−1. The analytical responses were obtained for the four electrodes. However, the best low limit detection and reproducibility was found for boron doped nanocrystalline diamond electrodes (BDND) doped with 2000mgL−1 in B/C ratio.

Molecularly Imprinted Polypyrrole Based Impedimentric Sensor for Theophylline Determination

In this study development of impedimetric sensor based on oxygen terminated boron-doped nanocrystalline diamond (B:NCD:O) modified with theophylline imprinted polypyrrole is described. Hydrogen peroxide induced chemical formation of polypyrrole molecularly imprinted by theophylline was applied for the modification of conducting silicon substrate covered by B:NCD:O film. Non-imprinted polypyrrole layer was formed on similar substrate in order to prove efficiency of imprinted polypyrrole. Electrochemical impedance spectroscopy was applied for the evaluation of analyte-induced changes in electrochemical capacitance/resistance. The impact of polymerization duration on the capacitance of impedimetric sensor was estimated. A different impedance behavior was observed at different ratio of polymerized monomer and template molecule in the polymerization media. The influence of ethanol as additive to polymerization media on registered changes in capacitance/resistance was evaluated. Degradation of sensor stored in buffer solution was evaluated.

Ultra-thin nanocrystalline diamond membranes as pressure sensors for harsh environments

Glass and diamond are suitable materials for harsh environments. Here, a procedure for fabricating ultra-thin nanocrystalline diamond membranes on glass, acting as an electrically insulating substrate, is presented. In order to investigate the pressure sensing properties of such membranes, a circular, highly conductive boron-doped nanocrystalline diamond membrane with a resistivity of 38 mΩ cm, a thickness of 150 nm, and a diameter of 555 μm is fabricated in the middle of a Hall bar structure. During the application of a positive differential pressure under the membrane (0–0.7 bar), four point piezoresistive effect measurements are performed. From these measurements, it can be concluded that the resistance response of the membrane, as a function of differential pressure, is highly linear and sensitive.

Boron doped diamond biotechnology: from sensors to neurointerfaces

Boron doped nanocrystalline diamond is known as a remarkable material for the fabrication of sensors, taking advantage of its biocompatibility, electrochemical properties, and stability. Sensors can be fabricated to directly probe physiological species from biofluids (e.g. blood or urine), as will be presented. In collaboration with electrophysiologists and biologists, the technology was adapted to enable structured diamond devices such as microelectrode arrays (MEAs), i.e. common electrophysiology tools, to probe neuronal activity distributed over large populations of neurons or embryonic organs. Specific MEAs can also be used to build neural prostheses or implants to compensate function losses due to lesions or degeneration of parts of the central nervous system, such as retinal implants, which exhibit real promise as biocompatible neuroprostheses for in vivo neuronal stimulations. New electrode geometries enable high performance electrodes to surpass more conventional materials for such applications.

Biocompatibility and electrochemical assessment of boron doped nanocrystalline diamond electrodes for neural stimulation

Event Abstract Back to Event Biocompatibility and electrochemical assessment of boron doped nanocrystalline diamond electrodes for neural stimulation Cristian P. Pennisi1*, Maria Alcaide1, Stavros Papaioannou1, Suzan Meijs2, Andy Taylor3, 4, Milos Nesladek5 and Vladimir Zachar1 1 Aalborg University, Dept. of Health Science and Technology, Denmark 2 Aalborg University, Dept. of Health Science and Technology, Denmark 3 ASCR, Institute of Physics, Czechia 4 NANO6, Czechia 5 University Hasselt, IMEC, Belgium Neural prostheses are devices that use electrical impulses to restore sensory or motor deficits following trauma or neurological diseases. In implanted devices, electrodes located in close proximity to the neural tissue are in charge of delivering the electrical impulses generated in a stimulation unit. The electrodes for neural stimulation possess one or various contact sites comprising a metal, such as platinum or iridium oxide, or a ceramic, such as titanium nitride (TiN). Although these are non-toxic materials with excellent electrochemical properties, many of the currently used designs display a compromised long-term performance as a result of the foreign body reaction. The growth of encapsulation tissue around the contact sites increases the distance between the electrode and neural cells over time. As a consequence, it is necessary to inject larger currents in order to achieve cell activation, which might exceed the potential at which oxidation and reduction of water takes place causing irreversible damage to the electrode and tissue. In recent years, nanocrystalline diamond (NCD) films have emerged as a unique class of biomaterials, which hold promise for the fabrication of neural electrodes due to their chemical inertness, biocompatibility and outstanding electrical properties (Pennisi and Alcaide, 2014). In this talk, a series of studies assessing the biocompatibility and electrochemical performance of boron doped NCD films for application in neural stimulation electrodes is described. The fabrication of boron doped NCD test substrates and electrodes by microwave chemical vapor deposition is presented. Furthermore, surface characterization of these substrates by Raman spectroscopy and atomic force microscopy is shown. Results of in vitro studies using the test substrates comprise protein adsorption, cytotoxicity, and cell proliferation and adhesion assays. These results are presented to describe the effects of the surface properties of the NCD films on the biological responses. We demonstrate that an increased surface roughness is crucial to significantly reduce adhesion and proliferation of fibroblasts on the NCD surfaces (Alcaide et al., 2014). The electrochemical performance and the in vivo biocompatibility of the boron doped NCD films are assessed using monopolar electrodes. It is shown that while electrical parameters such as impedance and charge injection capacity are similar to that of control TiN electrodes, NCD electrodes display a much wider water potential window, ranging from -1.7 to 1.4 V (Meijs et al.,2013). Data from the in vivo biocompatibility studies is also analyzed, consisting on the histological and histomorphometric assessment of the fibrous capsule after 2 and 4 weeks of subcutaneous implantation in a rat model. We show that implantation of NCD electrodes is associated with no signs of chronic inflammation and a very thin fibrous capsule, which after two weeks of implantation exhibit an average thickness of 25 μm. In summary, this talk presents data demonstrating that the proposed boron doped NCD electrodes can be safely operated within a wide potential window and cause a minimal foreign body reaction upon implantation. Taken together, these results indicate that boron doped NCD films represent a promising approach to mitigate the issues associated with fibrous encapsulation of neural stimulation electrodes Acknowledgements This work was supported by the EU through the project MERIDIAN (Micro and Nano Engineered Bi-Directional Carbon Interfaces for Advanced Peripheral Nervous System Prosthetics and Hybrid Bionics), contract n. 280778-02.

Processing of Nanoscale Gaps for Boron-doped Nanocrystalline Diamond Based MEMS

In this work we present a technological process flow enabling fabrication of transversal nanofeatures in nanocrystalline diamond based MEMS. Growth of thin diamond films on nanostructured templates, projection exposure lithography and bi-layer electron beam lithography are the key technologies used. Electrode gaps in the order of 100 nm have been successfully accomplished with suspended microplates with dimensions of 1×1 μm 2 .

Determination of the fungicide kresoxim-methyl in grape juices using square-wave voltammetry and a boron-doped diamond electrode

A square-wave voltammetric method for the determination of kresoxim-methyl in grape juices was developed using the nanocrystalline boron-doped diamond electrode where an irreversible oxidation occurred. Measurements were made through the anodic scan from +1000 to +1750mV (Maximum at +1420mV) in pH 4.0 acetate buffer 0.050molL−1. Linear signal response (R2>0.999) expanded form the 8.7×10−7molL−1 (0.27mgL−1) up to 3.4×10−5molL−1 (11mgL−1). The method was applied in the analysis of analyte fortified grape juices. Solid phase extraction allowed pre-concentration of the analyte and eliminated interferences imposed by sample matrix. Recoveries from 91.6% to 105.3% were found and agreed with results achieved using high performance liquid chromatography.