Nitrogen-incorporated Tetrahedral Amorphous Carbon Research Articles

The inner workings of sp2 clusters in nitrogen-incorporated tetrahedral amorphous carbon thin films according to optical analyses

The conduction mechanism in nitrogen-incorporated tetrahedral amorphous carbon (ta-C: N) thin films is mainly attributed to the conjugation in sp2 clusters. Here, ta-C:N thin films (about 100 nm) were deposited by laser controlled pulsed cathodic vacuum arc (Laser-Arc) at different nitrogen gas flow rates to investigate the electrical properties of such films. Mechanical and structural properties indicate an increase in sp2 fraction with a rise in nitrogen incorporation into the deposited films. However, after an initial decrease in electrical resistivity, it plateaus at higher flow rates while the sp2 content is still rising. Hence, to gain better understanding of the electronic properties, the dielectric constants ε1 and ε2 were obtained from the optical constants [n] and [k], which were numerically determined from reflectance [R] and transmittance [T] measurements in the wavelength range from 190 to 2500 nm (0.5 to 6.5 eV). The dielectric constant ε1 was used to calculate the dielectric volume of the atom, which is interpreted as a measure of the conjugated π electron system. Furthermore, modeling of the dielectric constants yielded the number of conjugated electrons per atom. Through the dielectric volume and number of conjugated electrons, it was discovered that the electrical conductivity does not only depend on the sp2 content and cluster size, but on how many electrons are conjugated and how much space these electrons occupy. The ta-C:N samples with the highest electrical conductivity, were either characterized by the largest occupied volume or the highest number of conjugated electrons.

HPLC−EC Analysis of Estrogenic Compounds: A Comparison of Diamond and Tetrahedral Amorphous Carbon Electrode Performance

AbstractHigh pressure liquid chromatography (HPLC) with amperometric detection was used to quantify estrogenic compounds in water samples. The main goal was to compare the detection figures of merit for boron‐doped diamond thin‐film (BDD) and nitrogen‐incorporated tetrahedral amorphous carbon (ta‐C : N) thin‐film electrodes. The target analytes were estrone, estradiol, and estriol. The BDD and ta‐C : N electrodes were investigated because of their excellent properties, which include a wide potential window, low background current, microstructural stability at high potentials, low limits of detection, weak molecular adsorption, fouling resistance and response reproducibility. ta‐C : N electrodes have not yet been investigated extensively in electroanalysis and are receiving increasing interest because they exhibit many of the excellent electrochemical properties of BDD electrodes and they can be deposited at room temperature by physical vapor deposition. The results reveal as low or lower background current and noise for the ta‐C : N electrode, as compared to the BDD electrode, and comparable or superior analytical detection figures of merit for all three emerging pollutants. The linear dynamic range for both electrodes was from 0.2 to 100 μmol L−1 for estriol, and 0.4 to 100 μmol L−1 for estradiol and estrone, and the sensitivity ranged from 9.1 to 11.2 mA mol L−1. For all three analytes, the limit of detection (S/N=3) ranged from 0.16–0.35 μmol L−1 (45‐95 ppb) for BDD and 0.20–0.34 μmol L−1 (58‐95 ppb) for ta‐C : N.

Evaluation of a nitrogen-incorporated tetrahedral amorphous carbon thin film for the detection of tryptophan and tyrosine using flow injection analysis with amperometric detection.

We report on the analytical performance of a tetrahedral amorphous carbon (ta-C:N) thin-film electrode in flow injection analysis with amperometric detection. Two model redox analytes were used to evaluate the electrode response because of their positive detection potentials and propensity (i.e., reaction products) to adsorb and foul sp2 carbon electrodes: tyrosine and tryptophan. ta-C:N electrodes are attractive for electroanalytical applications because they possesses many of the excellent properties of boron-doped nanocrystalline diamond (BDD) and they can be deposited at or near room temperature. The results show that the ta-C:N electrode exhibits lower background current and noise than glassy carbon (GC). The electrode was stable microstructurally at the positive potentials used for detection, ∼1.1 V, of these two amino acids and it exhibited superior analytical detection figures of merit as compared to GC and as good or superior to BDD. The linear dynamic range for both analytes at ta-C:N was from 0.1 to 100 μmol L-1, the sensitivity was 8-12 mA L mol-1, the short-term response variability was 1-2%, and the minimum detectable concentration was 89.7 ± 0.9 nM (18.3 μg L-1 or 0.46 ng) for tryptophan and 120 ± 11 nM (21.7 μg L-1 or 0.54 ng) for tyrosine. The analytical detection figures of merit for these amino acids at GC and BDD are also presented for comparison as is characterization data for the chemical composition and microstructure of the ta-C:N film.

Correction: Evaluation of a nitrogen-incorporated tetrahedral amorphous carbon thin film for the detection of tryptophan and tyrosine using flow injection analysis with amperometric detection.

Correction for 'Evaluation of a nitrogen-incorporated tetrahedral amorphous carbon thin film for the detection of tryptophan and tyrosine using flow injection analysis with amperometric detection' by Romana Jarošová, et al., Analyst, 2016, DOI: .

The Electrochemical Properties of Diamond and Tetrahedral Amorphous Carbon Electrodes in Room Temperature Ionic Liquids

Room temperature ionic liquids (RTILs) are emerging as a new medium for redox reactions as these liquids possess high solubilizing power, electrical conductivity, wide breakdown voltage and low volatility. Being composed entirely of ions (no solvent) and possessing wide electrochemical windows ( ca. 5 V), it is not difficult to see why these liquids are viewed by electrochemists to be attractive electrolytes for investigation. Our group is (i) studying the wetting of these ionic fluids on different carbon electrode surfaces and how this wetting affects the capacitance-potential relationships and (ii) investigating how the carbon electrode surface chemistry and microstructure affect the heterogeneous electron-transfer rate constant of different inorganic and organic redox systems in these ionic liquids. It is well established that the in aqueous electrolyte solutions, the heterogeneous electron-transfer rate constant for certain redox-systems at ordered HOPG and more microstructurally-disordered glassy carbon is strongly affected by the electrode surface microstructure and chemistry. We seek to learn if these same trends hold in ionic liquids. In this presentation, we will compare the electrochemical behavior of boron-doped nanocrystalline diamond and nitrogen-incorporated tetrahedral amorphous carbon thin-film electrodes. Specifically, contact angle measurements of the surface wettability, measurements of the double-layer capacitance (C dl) and its variation with potential, and heterogeneous electron-transfer rate constants for redox systems in structurally distinct RTILs will be presented. These two carbon electrodes have distinct microstructures as compared to their sp2 carbon counterparts. Nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) is a composite material consisting of a mixture of sp2 and sp3-bonded carbon. Impurities can be incorporated during growth (e.g., N) further adding to their complex structure. These films typically possess 40-60% sp3-bonded carbon. It has been widely used as a protective coating due to its hardness, high wear resistance and low coefficient of friction. The growth temperature for ta-C is usually from 25 to about 100 °C. This means that non-traditional materials, such as plastics, can be used as substrates for deposition. Importantly, these carbon materials possess some electrochemical properties that are similar to those of diamond.

Rapid Preparation of Room Temperature Ionic Liquids with Low Water Content as Characterized with a ta-C:N Electrode

Room temperature ionic liquids (RTILs) provide an ionic, solvent-free medium for electrochemical reactions. RTILs are appreciated for their many unique properties; nevertheless, it is precisely these qualities that can be very easily debased by water and organic impurities. Water, as a major contaminant in hygroscopic RTILs, has a strong effect on the physical and electrochemical properties (e.g., viscosity and dielectric constant, hence the background voltammetric current, diffusion coefficient of redox analytes and electron-transfer kinetics). In this work, a simple and relatively rapid purification process was investigated that involves sparging ultrahigh purity Ar through the RTIL while being heated at 70°C (so-called sweeping). A more conventional vacuum drying method at 80°C was used for comparison. The electrochemical properties of two RTILs, [BMIM][BF4] and [EMIM][BF4], were assessed voltammetrically using a nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) thin-film electrode. We found the sweeping purification method to be superior to vacuum drying in terms of more timely and effective removal of water. In addition, we present for the first time some of the basic electrochemical properties of novel ta-C:N electrode in contact with a RTIL.

Comparative electrochemical response of estrone at glassy-carbon, nitrogen-containing tetrahedral amorphous carbon and boron-doped diamond thin-film electrodes

The anodic oxidation of estrone was comparatively investigated at glassy carbon (GC), nitrogen-incorporated tetrahedral amorphous carbon (ta-C:N) and boron-doped diamond (BDD) electrodes. The ta-C:N and BDD electrodes are characterized by a wider working potential window and lower background current that for GC. The latter is because of a reduced level of pseudocapacitance on the former electrodes due to the absence of significant levels of redox-active surface carbon–oxygen functionalities. The irreversible oxidation of estrone was recorded at a similar potential for all three electrodes (0.9–0.95V) in 0.5molL−1 H2SO4. The voltammetric peak current decreased some for all the electrodes with potential cycling suggestive of some response attenuation by reaction product adsorption (or slow desorption). From the dependence of the oxidation peak potential and current with solution pH, it was possible to conclude that the electrooxidation of estrone involves the transfer of two electrons accompanied by the loss of two protons at pH<10. Voltammetric and chronocoulometric data indicated the oxidation reaction kinetics on all three electrodes were under mixed control by both diffusion and adsorption. This was most apparent for GC where estrone adsorption was greatest (145pmolcm−2). The greater adsorption on GC can be explained by electronic and or chemical effects associated with the graphitic edge plane sites. In contrast, the estrone adsorption on ta-C:N and BDD was significantly lower, about 1/10 of that on GC. This behavior is due to the differences in the types and density of functional groups and the absence of an extended π-electron system in both materials. In summary, the here-reported properties of the ta-C:N and BDD electrodes suggest that both could be excellent candidates for electroanalytical measurements involving the detection and/or determination of estrone and similar hormones.

Electrochemical Behavior of Gold Nanoparticles Modified Nitrogen Incorporated Tetrahedral Amorphous Carbon and Its Application in Glucose Sensing

Gold nanoparticles (NPs) with 10-50 nm in diameter were synthesized on nitrogen incorporated tetrahedral amorphous carbon (ta-C:N) thin film electrode by electrodeposition. The deposition and nucleation processes of Au on ta-C:N surface were investigated by cyclic voltammetry and chronoamperometry. The morphology of Au NPs was characterized by scanned electron microscopy. The electrochemical properties of Au NPs modified ta-C:N (ta-C:N/Au) electrode and its ability to sense glucose were investigated by voltammetric and amperometric measurements. The potentiostatic current-time transients showed a progressive nucleation process and diffusion growth of Au on the surface of ta-C:N film according to the Scharifker-Hills model. The Au NPs acted as microelectrodes improved the electron transfer and electrocatalytic oxidation of glucose on ta-C:N electrode. The ta-C:N/Au electrode exhibited fast current response, a linear detection range of glucose from 0.5 to 25 mM and a detection limit of 120 microM, which hinted its potential application as a glucose biosensor.

NEXAFS study and electrical properties of nitrogen-incorporated tetrahedral amorphous carbon films

Tetrahedral amorphous carbon nitride (ta-C:N) films obtained by filtered cathodic vacuum arc deposition have been investigated by Near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The C K (carbon K) edge NEXAFS spectra clearly revealed the increase of C N bonds with the increase of nitrogen concentration. The C K edge NEXAFS analysis further showed that the content of the surface defect (mainly C–H bonds) decreased with the increase of nitrogen in the films. As the nitrogen concentration increased a pronounced change in the π* features were observed at the N K (nitrogen K) edge. The origin of the N K edge π* peaks are mainly due to the formation of C N bonds and nitrogen substitution in the graphite network. Polarization dependent NEXAFS measurements showed an angular distribution of CN bonds. The electrical resistivity of the ta-C:N films decreased at higher nitrogen concentration and this may be from the development of graphite-like structures in these films. The electrical measurements were confirmed further with electrochemical measurements.

Dopamine and Ascorbate Analysis at Hydrodynamic Electrodes of Boron Doped Diamond and Nitrogen Incorporated Tetrahedral Amorphous Carbon

Rotating and hydrodynamically modulated rotating disk electrodes of boron-doped diamond (BDD) and tetrahedral amorphous nitrogen incorporated carbon (taC : N) were employed to extend analytical sensitivity and linear current response of these materials for dopamine analysis at physiological pH to 200 nM. Hydrodynamically modulated rotating disk electrode (HMRDE) techniques discriminate against nonmass transfer limited components, allowing more complete implementation of the wider electrochemical window of these materials. Experiments performed in the presence of ascorbate showed typical catalytic enhancement of the dopamine oxidation current and a corresponding loss of response to dopamine quinone at the ring in a rotating ring-disk electrode (RRDE) configuration. Utilizing these phenomena, a RRDE method for simultaneous determination of both dopamine and ascorbate concentrations in solutions containing comparable levels of both species is presented.

Electrodeposition and Nucleation of Copper at Nitrogen-Incorporated Tetrahedral Amorphous Carbon Electrodes in Basic Ambient Temperature Chloroaluminate Melts

The electrodeposition of copper on the atomically smooth nitrogen-incorporated tetrahedral amorphous carbon (taC:N) electrode has been studied in basic ambient temperature chloroaluminate melts. A high overpotential for nucleation of copper on taC:N and no underpotential deposition features are observed, comparable to the behavior of boron-doped diamond electrodes. Electrochemical deposition and stripping of copper on taC:N show that most of the deposit is anodically dissolved only when the potential reaches that of Cu(I) oxidation in a system in which Cu(I) and Cu(II) are both stable. The low density of intrinsic active sites for nucleation and its early saturation with increasing overpotential are responsible for the slight deviation from a model of the ideal progressive type of nucleation at high overpotentials. © 2001 The Electrochemical Society. All rights reserved.

Electrodes of Nitrogen-Incorporated Tetrahedral Amorphous Carbon A Novel Thin-Film Electrocatalytic Material with Diamond-like Stability

Electrodes of conductive nitrogen‐incorporated tetrahedral amorphous carbon films deposited at ambient temperatures are shown to possess an extraordinary combination of the stability associated with boron‐doped diamonds and greatly enhanced electrocatalytic properties. In this first communication on the electrochemistry of deposited thin films of , we show that this material demonstrates more active charge transfer properties on a variety of systems relative to the , highly boron‐doped diamond . Stability is shown by chlorine evolution from solution for times the coulombs necessary for oxidation to of a thick film without noticeable change of the voltammetry. Propitious attributes result from the high nitrogen content coupled with the mixed character of the amorphous semiconductor, which can be deposited at room temperature on practically any substrate. ©1999 The Electrochemical Society