Doped Diamond Research Articles

(Invited) High Power Diamond Devices with 2-D Transport Channels

Diamond transistors with surface 2D conduction channels are projected to be radiation hard with respect to neutrons. However, ionizing radiation hardness may be a problem due to the disruption of the 2D hole concentration. In this paper, the processing of three terminal devices with 2D surface conducting channels is presented as well as analysis of device transfer characteristics. This paper addresses the fabrication, radiation induced defects and device characteristics of microwave power field effect transistors (FET) built on 1) high quality diamond surfaces exploiting the 2 dimensional surface conductivity, and 2) the surface two dimensional “hydrogen terminated” conduction layer in diamond single crystals grown by CVD. Diamond is an ultra-wide bandgap semiconductor material that exhibits a number of ideal properties for future power and RF electronics applications beyond the current generation of SiC- and GaN-based technology. These properties include a bandgap of 5.5 eV, a high breakdown field (>10 MV/cm), high theoretical room-temperature carrier mobilities (>3800 cm2/V*sec), extremely high thermal conductivity (>22 W/cm*K), and excellent mechanical and thermal stability in vacuum. However, diamond doping is difficult, as the activation energies for typical dopants (B, P) exceed 0.37 eV and lead to very low dopant activation levels.[3] This drawback of dopant activation efficiency has been, in part, mitigated by two-dimensional conductivity found in hydrogen-terminated diamond surfaces. Hydrogen-termination (usually accomplished via exposure to hydrogen plasma) has been found to create a C-H surface dipole layer that reduces the carrier ionization energy by nearly 1.5 eV. Adsorbed species, such as atmospheric H2O, NO2, or intentionally-introduced passivation species contact this dipole layer, and together generate a two-dimensional hole gas (2DHG) with 1013-1014 holes/cm2 carrier density several nanometers below the diamond surface. Hydrogen-terminated diamond has been used as the basis for metal-semiconductor field effect transistors (MESFETs) and metal-oxide-semiconductor field effect transistors (MOSFETs) hydrogen-terminated diamond. Both unpassivated and passivated surface conduction devices have been fabricated. In the case of unpassivated devices, exposure to air (and thus atmospheric H2O) causes the devices to exhibit sheet charge densities in the 1013 holes/cm2 range.[1] MESFETs typically rely on Au metal for Ohmic contacts and Al metal for Schottky contacts to the hydrogen-terminated diamond. These devices have been normally-on devices, with threshold voltages around between -1V to +1V, depending on device dimensions.[1-4] MOSFETs fabricated using atomic layer deposited (ALD) oxides such as Al2O3 have been fabricated with either normally-off or normally-on behavior, depending on thermal history. Annealing of these devices at 180°C caused the devices to switch from normally-on to normally-off, with threshold voltages again in the range of ±1V range; the change was likely due to the removal of adsorbed species in the unpassivated diamond surfaces between the source, gate, and drain regions in the device, causing a reduction in the 2DHG sheet carrier density.[4] The diamond materials and surface preparation supplied by Euclid Techlabs using proprietary processes to produce defect free, ultra-smooth (Sa ~ 0.2 nm) diamond surfaces and buried boron ‘delta doped’ CVD layers. Euclid techlabs has demonstrated the delta doped transport channels in Diamond have mobilities in excess of 700 cm2/V sec. Device design and process science development was carried out within the facilities of the UMD NanoCenter and the NanoFab Lab. Radiation testing has been carried out at the radiation facilities of the University of Maryland. Device electrical performance and characterization has been carried out. We perform baseband noise, as well transconductance/output resistance dispersion characterization of 2D Surface Channel Diamond FETs fabricated under different processes and having different geometry and designs in order to identify device defects and their reliability and their susceptibility to radiation effects. The impact of the various types of noise on device defect and radiation hardness will be reported. Materials characterization techniques including Raman spectroscopy (strain, sp2 vs sp3 bonding), FTIR, and SIMS. Common diamond point defects are characterized by photoluminescence and FTIR.

Polymer-Coated Boron Doped Diamond Optically Transparent Electrodes for Spectroelectrochemistry

Spectroelectrochemistry is a well-known technique used to achieve multimode selectivity in one sensor. The sensor usually consists of an optically transparent electrode (OTE) coated with a charge selective polymer film. These polymer films are employed to pre-concentrate analyte at the OTE surface so that it can be sufficiently detected optically through electrochemical modulation. OTEs such as Indium Tin Oxide (ITO) have been used extensively in this method but little is known about the applicability of such sensors using other OTE materials, such as Boron Doped Diamond (BDD). One distinct advantage of BDD OTEs over ITO OTEs is their significant increase in sensitivity for organic compounds, such as para-aminophenol and hydroquinone. With this, we have developed absorption and fluorescence-based sensing methods with a BDD OTE coated with a sulfonated ionomer film, Nafion. This is demonstrated with tris(2,2’-bipyridyl)ruthenium(II) ion [Ru(bpy)32+] using an attenuated total reflectance (ATR) flow cell setup for both absorbance and fluorescence. With a Nafion coated BDD optically transparent thin layer electrode (OTTLE), we developed a fluorescence based sensor for a common polyaromatic hydrocarbon (PAH), 1-hydroxypyrene (1-pyOH), achieving a detection limit of 80 nM (17 ppb). Using these techniques, we were able to manifest new sensing applications while broadening the use of spectroelectrochemistry, OTEs, and BDD as an electrode material. Figure 1

Resistivity Characterization of Solid Electrolyte Interphase on Lithium Ion Battery Silicon Anodes

Lithium-ion battery (LIB) technology plays a critical role the clean energy sector, with applications in electronic devices, electric and hybrid vehicles, and stationary energy storage. In order to improve battery efficiency and performance, novel materials must be developed and studied. Battery anode materials are of particular interest, and silicon has been selected for materials research due to its high theoretical storage capacity as well as the extensive existing knowledge regarding silicon material processing and fabrication. The initial cycling of a LIB, regardless of anode material, results in the formation of a solid electrolyte interphase (SEI) layer between the electrolyte and the anode. This passivating layer, consisting of decomposition products from the electrolyte solution, is critical to the reliability and performance of the battery. The SEI must be both electronically insulating and ionically conductive: permeable to lithium ions yet resistant to electron flow. The resistance can be inhomogeneous along the anode plane or perpendicular to it. To our knowledge, no characterization technique has been capable of measuring spatial variation in SEI resistivity. In order to measure SEI resistivity with nanometer-scale resolution, our group has utilized scanning spreading resistance microscopy (SSRM) with a specialized atomic force microscopy (AFM) system installed in an argon glove box to minimize sample exposure to oxygen and water. The setup employs a doped diamond coated silicon probe that exhibits high wear resistance and low electronic resistance. Through application of a sample-probe bias voltage while utilizing variable forces on the probe in AFM contact mode, the technique allows for the measurement of SEI resistivity laterally and vertically. The vertical depth of measurement is controllable by the applied probe force (as well as raster scan line density) and is thus capable of milling away SEI material to measure resistivity at defined depths. Subsequent AFM height measurement allows for measured resistance to be associated with the depth of measurement. The electronic system attached to the system measures current through the probe-sample with a logarithm-scale amplifier, which can be directly converted to resistance or resistivity. Our measurements of resistance vs. depth for SEIs formed on single-crystal silicon wafers [001] after a single cycle of lithiation/delithiation demonstrate strong trends for decrease in resistance as the probe penetrates deeper levels of the SEI. Such plots provide an interesting basis for the study of SEIs formed under different cycling conditions with distinct electrolyte solutions. Figure: (a) Schematic diagram of electronic setup of the described system, (b) resistance map at a depth of 43 nm on a SEI formed on a single-crystal silicon wafer [001], with a single cycle of lithiation (0.01 V for 5 hours) and delithiation (1.0 V for 5 hours) in a battery cell containing ethylene carbonate (EC) and diethyl carbonate(DEC) electrolytes, (c) topography map displaying the SEI depth of resistance mapping. Figure 1

Electrolyzed Water for Selective Etching of Metals

Electrolyzed water (EW) is a promising tool for wet cleaning of semiconductor devices. At the anode, hydroxyl radicals exhibiting a very high oxidation reduction potential (ORP) are produced, generated by electrodes made of materials with high overpotential. Thus, water with high ORP is obtained, which can be higher than the ORP of thermodynamically stable water. In comparison, cleaning solutions made of a mixture of chemicals, such as SC2-solutions, are always within the thermodynamic boundaries. The high ORP of electrolyzed anodic water (AW) is advantageous concerning some issues in IC fabrication, such as its stability in contrast to the change of dilution in SC2-solutions by decomposition of H2O2. Furthermore, an enhanced ORP is beneficial for the removal of metal contamination. In this concern the choice of the electrode material is crucial. For example, platinum electrodes tend to dissolve in the AW and cause contamination during the wet cleaning process. However, electrodes coated with boron doped diamond (BDD) are protected by the BDD layer and thus, there is no contamination of the EW. Indeed, one option for wet cleaning during semiconductor production is particle removal from silicon wafers. For this application, electrolyzed cathodic water (CW) has been applied for already several years to improve the removal of particles smaller than 50 nm [1, 2, 3]. Additionally to CW, Red Ox® cell technology is able to provide various types of EW for different process specifications and applications in semiconductor industry. Water can be processed through either the cathodic side or the anodic side of the cell producing CW, hydrogenated water (HW), ozonized water (OW), anodic water fluoride (AW-F), anodic water chloride (AW-Cl) or anodic water sulphate (AW-SO4), depending on the feed solution. For photo resist removal electrolyzed sulphuric acid (ESA) can be used. In this study, the application of AW in the selective etching of metals is shown. The pH value and the corresponding ORP values of the AW can easily be controlled by adjusting the current and reaction time of the electrolysis. Metal etching rates of AW were determined for four different metals with respect to pH. Based on the results it becomes clear, that the etching rates for different metals vary significantly on the pH and corresponding ORP of the AW. This means, that by a careful selection of the pH/ORP value, the etching rate of the metal can be adjusted. Furthermore, the etching selectivity for different metals allows for defined etching of one material without the loss of another material. These results indicate that the electrolyzed water chemistry with a dedicated pH/ORP value is a promising tool for wet chemical cleaning of metal contaminations. Tab. 1: Various types of electrolyzed water (EW), which can be produced for different kinds of wet cleaning applications. [1] K. Ryoo and B. Kang: Electrolyzed water as an alternative for environmentally-benign semiconductor cleaning chemicals. CLEAN TECHNOLOGY, 7 , p. 215-223(2001). [2] G. Choi: Necessity of cleaning and its Application in Future Memory Devices. Solid State Phenomena, 219, p. 3-10 (2015). [3] M. Fryda, Th. Matthée, J. Oshinowo, D.H. Baek, H.-J. Förster and G. Heinze: Operation of a new electrolyzed cell using Boron Doped Diamond electrodes. Solid State Phenomena, 2192, p. 40-43 (2015). Figure 1

Impact of Thermal Treatments in Crystalline Reconstruction and Electrical Properties of Diamond Ohmic Contacts Created by Boron Ion Implantation

To obtain p‐type doping of diamond through B ion implantation, thermal treatments are necessary to reconstruct the diamond lattice and to locate B atoms in substitutional lattice positions. The present contribution evaluates by STEM‐EELS and CL spectroscopy the amorphisation of diamond lattice under the B+ bombardment and its subsequent reconstruction after the thermal treatment. In addition, TEM observations allowed localizing the boron spatial distribution. Carbon‐related peaks of EELS spectroscopy shows a nearly complete recovery of the diamond lattice after thermal treatment. Indeed, at 1600 °C, sp2/sp3 ratio in implanted regions changes from 0.56 to 0.18 (0.15 value was measured before implantation). On the other hand, CL spectroscopy reveals how A‐Band and free exciton emission peaks, which are quenched by B+ implantation, recover after annealing. Boron ion implantation was used to create ohmic contacts in two different diamond samples, treated with different annealing velocities. Crystalline reconstruction, evidenced by TEM data explains the related electric behaviour. Nanoscale evidences of amorphisation, lattice reconstruction and dopant activation are presented and discussed in this work.

Pressure-Temperature-Induced Transformations of Hydrocarbon- Fluorocarbon Mixtures into Nano- and Micron-Size Diamonds

Studies of thermal transformations of naphthalene (С10Н8), fluorographite (CF1.1) and octafluoronaphthalene (С10F8) and their binary mixtures (С10Н8 – CF1.1, С10Н8 – C10F8) under pressure of 8 GPa have been undertaken as models for gaining understanding of processes of carbonization, graphitization and diamond formation in pure hydrocarbon, fluorocarbon and carbon-hydrogen-fluorine-containing systems under high pressures. The studies found a significant reduction in the initiation temperature thresholds for all major thermal transformation processes in case of binary mixtures with respect to thresholds for pure hydrocarbon and fluorocarbon compounds. Another distinctive feature of the transformations of binary mixtures with respect to diamond formation stage of the transformations of pure hydrocarbons, has been the presence of massive quantity of nanosize (10–60 nm) diamond fraction in the products from binary mixtures along with the micron-size (5–20 μm) diamond fraction, typically observed in the transformations of pure hydrocarbons. The origin of nanodiamond was related to the specifics of carbonization of fluorocarbon compounds under pressure, which at 800–1000 °С produces, along with submicron particles of graphite-like material, a significant amount of closed shell 2–5 layer carbon nanoparticles of 5–15 nm size. These onion-like carbon nanoparticles act as precursors for formation of nano size diamond fractions in the transformations of binary mixtures of hydrocarbon and fluorocarbon compounds. These results potentially open a new direction for metal catalyst-free synthesis of pure and doped diamonds for broad applications. The present article gives an overview of this emerging area of rese arch.

ZnO Electrodeposition on Boron-Doped Diamond: Effects of Diamond Surface Terminations

Diamond and zinc oxide (ZnO) are two highly important, wide band gap, semiconductors with a great number of attractive properties. Recently the combination of n-type ZnO and p-type diamond has attracted much attention for different applications as the fabrication of heterojunctions [1], surface acoustic-wave (SAW) devices [2] or biosensors electrodes [3]. In these works, ZnO was mainly deposited on diamond surfaces by high temperature processes such as chemical vapor deposition (CVD) [4], magnetron sputtering [5] or atomic layer deposition (ALD) [6]. Electrochemical deposition (ECD) is emerging as an important method to prepare semiconductor thin films such as ZnO. This chemical route presents many advantages such as low cost, low temperature, soft processing of materials and possibility to obtain a large range of structures from dense layers up to well-defined nanostructures by means of appropriate growth parameters. Since the last decades, the electrodeposition of ZnO has been successfully performed on many conductive substrates [7] leading to the growth of various structures but it was studied only one time on diamond from a Zn(NO3)2solution [8]. Whatever the process, the first step in the ECD of ZnO consists in the production of hydroxides near the electrode surface to raise the local pH. Three precursors can be used to produce the OH- ions: Hydrogen peroxide, nitrate salts or dissolved oxygen. Unlike zinc nitrate, using oxygen as a precursor allows the modulation of [OH-]/[Zn2+] ratio in the bath. Recently our group has thus investigated the ECD of ZnO on Boron Doped Diamond (BDD) electrodes using the method based on the reduction of dissolved O2, developed by Peulon and Lincot [9]. The reduction of dissolved oxygen leads to the formation of hydroxide (step (1) or (1)’), by raising the local pH the precipitation of zinc hydroxide (step (2)) occurs in presence of Zn2+ions, which is finally transformed into zinc oxide by dehydration (step (3)). O2 + 2 H2O + 4 e- → 4 OH- (1) O2 + 2 H2O + 2 e- → H2O2 + 2 OH- (1)’ Zn2+ + 2 OH- → Zn(OH)2 (2) Zn(OH)2 → ZnO + H2O (3) We studied the influence of bath temperature and zinc chloride concentrations and evidenced that the ECD of zinc oxide was promising on as-grown H terminated BDD electrodes [10, 11]. In the present work, we focus on the influence of the BDD surface chemistry either H- or O-terminated obtained by different oxidation treatments (electroless [12] or anodic [13]) on the ZnO deposition process. Surface terminations are followed by contact angle measurments and XPS analyses. The morphologies and structures of ZnO deposits are characterized by XRD and SEM. Besides playing on deposit morphology, this work shows that the surface terminations of BDD (-CH, -CHx, C-OH, -COOH, -COC or -C=O) have also a strong effect on the ZnO deposit adhesion. [1] Wang, C. X.; Yang, G. W.; Zhang, T. C.; Liu, H. W.; Han, Y. H.; Luo, J. F.; Gao, C. X.; Zou, G. T. Diam. Relat. Mater. 2003, 12, 1548–1552. [2] Luo, J. T.; Zeng, F.; Pan, F.; Li, H. F.; Niu, J. B.; Jia, R.; Liu, M. Appl. Surf. Sci. 2010, 256, 3081–3085. [3] Zhao, Z.; Lei, W.; Zhang, X.; Wang, B.; Jiang, H. Sensors (Basel). 2010, 10, 1216–1231. [4] Sang, D.; Li, H.; Cheng, S. Appl. Surf. Sci. 2011, 258, 333–336. [5] Yu, Q.; Li, H. D.; Zou, G. T. Diam. Relat. Mater. 2011, 20, 351–354. [6] Hikavyy, a.; Clauws, P.; Vanbesien, K.; De Visschere, P.; Williams, O. a.; Daenen, M.; Haenen, K.; Butler, J. E.; Feygelson, T. Diam. Relat. Mater. 2007, 16, 983–986. [7] Lincot, D. Thin Solid Films 2005, 487, 40–48. [8] Chatterjee, A.; Foord, J. Diam. Relat. Mater. 2006, 15, 664–667. [9] Peulon, S.; Lincot, D. 1996, 05, 166–170. [10] P. Gautier, A. Vallee, C. Sinito, A. Etcheberry, N. Simon , Diam. Relat. Mater. 2016, 62, 1–6 [11] P. Gautier, A. Vallee, A. Etcheberry, N. Simon, , Electrochem. Soc. Trans.2015, 66 (6) 141-149. [12] N. Simon, G. Charrier, A. Etcheberry, Electrochimica Acta. 2010, 55, 5753 [13] H.A. Girard, E. de La. Rochefoucauld, D. Ballutaud, A. Etcheberry and N. Simon, Electrochem. Solid State Lett. 2007,10, F34

Heavily Boron Doped Diamond Electrodes for Ultra Sensitive Determination of Ciprofloxacin in Human Urine

AbstractCiprofloxacin is one of the most potent fluoroquinolone antibiotics in medical treatment with a widely effective antibacterial activity. Aim of the presented paper was to use boron doped diamond electrodes for a sensitive, simple and reliable voltammetric determination of ciprofloxacin in human urine samples. Prior to the electrochemical analyses, an optimal boron doping level was determined in order to achieve the highest sensitivity. A set of boron doped diamond electrodes with the doping level in the range from 0 to 20 000 ppm B/C was used for this purpose. Electrochemical behavior of ciprofloxacin was investigated using cyclic voltammetry in an ammonium acetate buffer (pH 5), where ciprofloxacin provided a well‐defined irreversible oxidation peak at a potential of + 1.15 V. Under optimal experimental conditions, the calibration curve obtained by square‐wave voltammetry was linear in a concentration range from 0.15 to 2.11 μmol/L (R2=0.9974). A very low limit of detection (0.05 μmol/L) was obtained for the BDD electrode with the highest doping level. The developed square wave method was successfully applied to the determination of ciprofloxacin in human urine samples with a very good recovery (from 97 to 102%).

X-ray absorption fine structure study of heavily P doped (111) and (001) diamond

X-ray absorption fine structure (XANES) measurements were carried out for P doped (111) and (001) diamond films, and the results were compared with those from simulations. For the (111) spectrum, the main strong peak observed at 2147.0 eV and three broad peaks centered at 2150 eV, 2157 eV, and 2165 eV were observed. The assignment with the estimation by the simulation of the XANES peaks showed the interstitial sites additional to the substitutional site. The Extended X-ray Absorption Fine Structure (EXAFS) result of the P doped (111) diamond showed that the first and second neighboring peaks are observed at 1.21 A and 2.0 A, respectively. The assignment with the estimation by the simulation of the EXAFS peaks also showed the interstitial sites additional to the substitutional site. Overall, P in diamonds presumably has dopant sites in both the substitutional and interstitial sites.

First-principles calculation of a negatively charged boron-vacancy center in diamond

As the boron doping in diamond has been well established, and a negatively charged boron-vacancy (BV) center has an active electron paramagnetic resonance, the BV center is an attractive candidate for spin information devices. Using the first-principles calculation, we report the electronic structure of the BV center in diamond for its various charge states. A geometrically optimized BV center in the diamond supercell exhibited C3v symmetry. The BV+1 charge state did not exhibit any spin splitting defect levels, while the BV0 and BV−2 charge states showed a small energy separation between spin-polarized states. On the other hand, the negatively charged BV−1 center possesses bound states with a larger separation inside the diamond bandgap. Moreover, it has the spin-triplet ground state and the spin-conserved triplet excited state. These characteristics indicate that the BV−1 center in diamond is a good candidate for qubit operation.

From micro to nanocrystalline boron doped diamond applied to cadmium detection

Cadmium detection was investigated by Square Wave Anodic Stripping Voltammetry (SWASV) measurements by using boron doped diamond electrodes with different morphologies from micro to nanocrocrystalline grains as Boron Doped Diamond (BDD) and Boron Doped Nanocrystalline Diamond (BDND), respectively. The argon concentrations, in the argon/hydrogen ratio, used were 0, 50, 60, 70, and 80vol.%. SWASV technique was applied in 4×10−4mol L−1 ammonium acetate buffer pH4.2. The peak currents were measured for Cd2+ concentration ranging from 1 to 20μgL−1. This change in film grain size and roughness affected how cadmium was deposited on the electrode surfaces, thus affecting its electroanalytical response from SWASV measurements as well as its selectivity. For all electrodes cadmium detection limits (DL) were lower than 1μgL−1 while for BDND electrode DL reached 0.016μgL−1. These values are lower than that required by the Brazilian Health Ministry for potable water (1μgL−1) and confirm that diamond electrodes are a suitable mercury-free method to determine cadmium trace levels in water. A strong correlation between the electrode selectivity and its grain size also confirmed the best performance of BDND electrode.

Erbium ion implantation into diamond - measurement and modelling of the crystal structure.

Diamond is proposed as an extraordinary material usable in interdisciplinary fields, especially in optics and photonics. In this contribution we focus on the doping of diamond with erbium as an optically active centre. In the theoretical part of the study based on DFT simulations we have developed two Er-doped diamond structural models with 0 to 4 carbon vacancies in the vicinity of the Er atom and performed geometry optimizations by the calculation of cohesive energies and defect formation energies. The theoretical results showed an excellent agreement between the calculated and experimental cohesive energies for the parent diamond. The highest values of cohesive energies and the lowest values of defect formation energies were obtained for models with erbium in the substitutional carbon position with 1 or 3 vacancies in the vicinity of the erbium atom. From the geometry optimization the structural model with 1 vacancy had an octahedral symmetry whereas the model with 3 vacancies had a coordination of 10 forming a trigonal structure with a hexagonal ring. In the experimental part, erbium doped diamond crystal samples were prepared by ion implantation of Er+ ions using ion implantation fluences ranging from 1 × 1014 ions per cm2 to 5 × 1015 ions per cm2. The experimental results revealed a high degree of diamond structural damage after the ion implantation process reaching up to 69% of disordered atoms in the samples. The prepared Er-doped diamond samples annealed at the temperatures of 400, 600 and 800 °C in a vacuum revealed clear luminescence, where the 〈110〉 cut sample has approximately 6-7 times higher luminescence intensity than the 〈001〉 cut sample with the same ion implantation fluence. The reported results are the first demonstration of the Er luminescence in the single crystal diamond structure for the near-infrared spectral region.

The Kinetic Parameters of the Oxygen Evolution Reaction (OER) Calculated on Inactive Anodes via EIS Transfer Functions: •OH Formation

The electrocatalytic behavior of “inactive” (Boron Doped Diamond (BDD), SnO2-Sb and PbO2) anodes toward the oxygen evolution reaction (OER) is evaluated using dc and ac techniques, under controlled experimental conditions (e.g. air bubbling, ohmic drop correction). Tafel slopes estimated from anodic polarization curves for all catalysts are located above 100 mV dec−1, suggesting that the rate-controlling step is similar for these materials at determined overpotentials. In agreement with the literature, it could be associated with the •OH generation since “active catalysts” displays slopes below 80 mV dec−1. A transfer function model is derived to account for the kinetic parameters of the OER mechanism for each anode, throughout its fitting to experimental electrochemical impedance spectroscopy (EIS) spectra. The model considers the kinetics of each elementary reaction and the material balances for the rates of formation of the adsorbates (H2Oads, •OHads, •Oads, •OOHads, and O2ads) involved in the OER. It is found that the rate-controlling step on SnO2-Sb (≤2.14 V), PbO2 (≤1.74 V) and BDD (2.54–2.71 V) is associated with the •OH formation, while this control is only modified when the potential becomes more positive for the oxide catalysts, thus, being determined by the production of adsorbed oxygen O2ads which on its turn promotes the O2 evolution. On the other hand, the rate-control step remains similar for BDD over the entire analyzed potential range, standing out its unique properties as inactive catalyst of the OER.

<italic>V</italic>2O5MISFETs on H-Terminated Diamond

We report for the first time on the dc and RF performance of novel MISFETs fabricated on hydrogen-terminated (H-terminated) single crystal diamond film using vanadium pentoxide (V2O5) as insulating material. The active devices were characterized in terms of static $I$ – $V$ characteristics and static transconductance as well as of S-parameters for the calculation of the maximum cutoff frequency and the maximum oscillation frequency. Time stability of the drain current was evaluated overnight observing a maximum fluctuation of 7%. Investigations on temperature dependence of diamond-based MISFET were also performed up to 130 °C. The experimental results were compared with the better established diamond MESFET technology. Finally, the surface transfer doping of H-terminated diamond by very thin V2O5 insulator was also investigated in terms of conductivity, stability in air, and resistance to high temperatures.

CO_2 laser micromachining of nanocrystalline diamond films grown on doped silicon substrates

We demonstrate that nanocrystalline diamond films grown on highly doped silicon substrates can be patterned using a CO2 laser operating at a wavelength of 10.6 μm, where both low doped silicon and diamond exhibit negligible optical absorption. The patterning is initiated by free carrier absorption in the silicon substrate and further enhanced by the thermal runaway effect, which results in surface heating in the silicon substrate and subsequent thermal ablation of the diamond film in an oxygen rich atmosphere. Using this approach, micron-scale grating and dot patterns are patterned in thin film diamond. The localized heating is simulated and analyzed using concurrent optical and thermal finite element modelling. The laser patterning method described here offers a cost effective and rapid solution for micro-structuring diamond films.

Electrochemical Transduction at Modified Boron Doped Diamond Interfaces

Innovation in nanoscience depends fully on the ability to synthesize nanomaterials as well as to assemble them efficiently into complex architectures. The discovery of graphene and graphene polymer nanocomposites is playing a key role in modern nanoscience and nanotechnology. Graphene oxide (GO), is a derivative of graphene obtained by the use of strong oxidizing agents to obtain graphene oxide, a nonconductive hydrophilic carbon material. Synthesis of graphene oxide was performed using the Hummers method. Graphene oxide was integrated into the polysulfone (PSF) matrix to form polysulfone/graphene oxide nanocomposite. Polysulfone casting suspension was prepared by dissolving polysulfone in N,N-dimethyl acetamide. The polymer composites consisted of homogeneously blended polysulfone and graphene oxide casting solutions and drop coated onto boron-doped diamond electrodes (BDD). Interfacial electrochemical dynamics were characterised using cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy were used to study the morphology and structure of the prepared materials. Modifying with polysulfone blocks electron transfer in the redox reaction of K3Fe(CN)6. PSF /GO enhances electron transfer even when compared to bare BDD. The diffusion coefficient and sensitivity for PSF-GO/BDD electrode was calculated to be 2.660 x10-4 cm2 s-1 and 6.7587 x10-6 mV s-1 / A.

Intermittent‐contact Scanning Electrochemical Microscopy (IC‐SECM) as a Quantitative Probe of Defects in Single Crystal Boron Doped Diamond Electrodes

AbstractWe demonstrate, for the first time, the use of electrochemical imaging to identify defect and defect free areas in single crystal boron doped diamond (BDD) electrodes. Specifically, we show that defects contain different boron dopant concentrations than the surrounding single crystal matrix and that these variations can be visualized using intermittent contact−scanning electrochemical microscopy (IC‐SECM). The measured IC‐SECM tip currents provide quantitative information on the rates of electron transfer across the single crystal BDD electrodes, which correlate with variations in boron doping levels. In some instances, IC‐SECM outperforms alternative methods such as Raman microscopy and cathodoluminescence imaging, due to its intrinsic surface‐sensitivity, expanding the application and impact of electrochemical microscopy for materials characterization. The results obtained, and procedure outlined, are particularly valuable for the assessment and screening of single crystal BDD electrodes.

High-performance non-enzymatic glucose sensor based on nickel-microcrystalline graphite-boron doped diamond complex electrode

A nickel-microcrystalline graphite-boron doped diamond (Ni-MG-BDD) complex electrode was fabricated by thermal catalytic etching BDD film with Ni layer. Scanning electron microscopy, energy dispersive X-ray spectrum and Raman spectroscopy were utilized to characterize the morphology, composition of the complex electrode, respectively. Nickel particles with different sizes are demonstrated to sink into the crystal facet and grain boundary of the BDD film, which not only increases the specific surface area and the electrochemical stability of the electrode, but also catalyzes sp3-bonded diamond into sp2-bonded microcrystalline graphitic carbon in the cooling process. The presence of microcrystalline graphite mixed with diamond film is confirmed to increase the conductivity of the electrode. Electrochemical results indicate that the Ni-MG-BDD complex electrode shows excellent electrochemical performance for glucose oxidation. The proposed electrode shows wide linear ranges for glucose concentrations of 0.002–0.5 and 0.5–15.5mM with high sensitivities of 1010.8 and 660.8μAmM−1cm−2, respectively. In addition, the electrode exhibits a low detection limit of 0.24μM (S/N=3), good selectivity and reproducibility, and excellent stability during the long-term electrochemical detection.

Statistical optimization of electrochemical oxidation of ethylene glycol using response surface methodology

Large amounts of ethylene glycol (EG) based antifreeze liquids are daily discharge into the receiving waters. The chemical oxygen demand (COD) detected in most of the lakes and rivers close to the discharge points exceeded 100,000mg O2/L. With such an amount, biological and chemical processes are inefficient to completely remove EG. In order to efficiently remove EG, electrochemical oxidation (ECO) of EG was carried out. Niobium Boron Doped Diamond (Nb/BDD) was used as anode whereas carbon felt was used as cathode. Different operating parameters including current intensity, treatment time, electrolyte concentration and pollutant concentration were tested. The application of 0.077A/cm2 of current density during 120min in the presence of 7.0g/L of Na2SO4 allowed 89.6±0.2% of COD removal with 490mg O2/L of residual COD. This result was far below the legislation standard set by the province of Quebec that allows the discharge of 800mg O2/L of COD. The efficiency of ECO process was attributed to both direct and indirect oxidation that generate strong oxidizing species (OH°, S2O82−, H2O2, etc.) capable of oxidizing organic matters on the surface of the anode and in the bulk of the solution.

Deposition and Characterization of Si-Doped Diamond Films Using Tetraethoxysilane onto a WC-Co Substrate

Silicon-doped (Si-doped) diamond films were deposited on a Co-cemented tungsten carbide (WC-Co) substrate using the hot filament chemical vapor deposition (HFCVD) method with a mixture of acetone, tetraethoxysilane (TEOS), and hydrogen as the recant source. The as-deposited doped diamond films were characterized with field emission scanning electron microscopy (FE-SEM), Raman spectrum, and X-ray diffraction (XRD). Furthermore, Rockwell C indentation tests were conducted to evaluate the adhesion of the Si-doped diamond films grown on the WC-Co substrate. The results demonstrated that the silicon concentration in the reactant source played an important role in the surface morphology and adhesion of diamond films. The size of diamond grain varied from 3 μm to 500 nm with silicon concentration increasing from 0 to 1.41 atom %. When the silicon concentration rose to 1.81 atom %, the grain size became bigger than that of the lower concentration. The ratio of diamond peak {220}/{111} varied with different silicon concentrations. Raman study features revealed high purity of as-deposited diamond films. The Raman spectra also demonstrated the presence of silicon in the diamond films with Si–Si, Si–C and Si–O bonds. Si-doped diamond films with strong adhesive strength on the WC-Co substrate was beneficial for diamond films applied on cutting tools and wear resistance components.