Doped Diamond Films Research Articles

Fabrication and high-temperature tribological performance of doped diamond film with B, N, and Si elements

The diamond film is prone to oxidation in environment above 600 °C, making it difficult to maintain good wear resistance at high-temperatures. The high temperature oxidation resistance of diamond films can be improved through multiple doping. However, its wear resistance and anti-friction performance during high-temperature processing remain to be studied. In this study, single-doped, co-doped, and multi-doped diamond films with B, N, and Si doping combinations were fabricated on the surface of cemented carbide substrates. Performance characterization and high-temperature friction experiments were carried out on these films. The results show that B-doping can enhance wear resistance at high temperatures, N-doping can improve hardness, and Si-doping can reduce the coefficient of friction (CoF) of the diamond film. The multi-doped diamond film exhibits a comprehensive improvement effect due to the combination of different doping elements. During the high-temperature friction process, its CoF is significantly lower than that of undoped diamond film, resulting in a relatively high surface finish of the silicon nitride ball friction against it. Additionally, its excellent high-temperature wear resistance leads to minimal grain wear on the film surface and a low degree of transition from diamond to graphite phase on the surface. This study provides valuable insights for the application of multiple doped diamond films in high-temperature processing.

Effects of oxygen/nitrogen co-incorporation on regulation of growth and properties of boron-doped diamond films

Regulation with nitrogen and oxygen co-doping on growth and properties of boron doped diamond films is studied by using laughing gas as dopant. As the concentration of laughing gas (N2O/C) increases from 0 to 10%, the growth rate of diamond film decreases gradually, and the nitrogen-vacancy (NV) center luminescence intensity increases first and then weakens. The results show that oxygen in laughing gas has a strong inhibitory effect on formation of NV centers, and the inhibitory effect would be stronger as the concentration of laughing gas increases. As a result, the film growth rate and nitrogen-related compensation donor decrease, beneficial to increase the acceptor concentration (∼3.2 × 1019 cm−3) in the film. Moreover, it is found that the optimal regulation with the quality and electrical properties of boron doped diamond films could be realized by adding appropriate laughing gas, especially the hole mobility (∼700 cm2/V⋅s), which is beneficial to the realization of high-quality boron doped diamond films and high-level optoelectronic device applications in the future.

Theoretical and experimental research on growth and doping mechanisms of diamond films fabricated using liquid carbon source precursors

Fabricating diamond films using liquid carbon source precursors in hot filament chemical vapor deposition (HFCVD) is an emerging technology. Although some experiments have demonstrated the feasibility of depositing doped diamond films using liquid carbon source precursors such as acetone, the theoretical explanation still needs to be elucidated. In this study, the density functional theory (DFT) method was used to analyze the decomposition and adsorption processes of acetone and methane on the surface of a diamond (111) models and to clarify the advantages of liquid carbon source precursors. The decomposition and adsorption reaction processes of trimethyl borate, urea, and ethyl orthosilicate on the surface of diamond (111) model were also analyzed to elucidate the doping mechanisms of B, N, and Si elements. Additionally, undoped diamond films were fabricated using acetone and methane precursors, illustrating that liquid precursors have higher growth rates than gas precursors. B-, N-, and Si-doped diamond films were also fabricated using liquid-doped carbon source precursors. Element detection by TOF-SIMS illustrates that all three elements had been doped into the diamond films and were uniformly distributed. Conversely, no doping elements were detected in N-doped diamond film fabricated with nitrogen and methane precursors.

Influence of boron doped level on the electrochemical behavior and seawater salinity detection of boron doped diamond film electrodes

Boron doped diamond (BDD) film electrodes have a good application prospect in the field of seawater salinity detection. However, the influence mechanism of boron doping level (given by B/C ratio) on seawater salinity detection limited its application. In this paper, microstructure-phase-electrochemical relationships in BDD film electrodes were systematically investigated, aiming to reveal the effect of boron content on seawater salinity measurement, and lay a foundation for practical application of BDD film electrodes. With the increase of the boron doping, the content of non-diamond phase increased, while the crystallinity and the grain size of diamond decreased. Meanwhile, when the B/C ratio of BDD electrode reached 10000 ppm, they had the largest electroactive surface areas (EASA) and the smallest diffusion resistance, and their electrochemical performance was optimal in this study. In addition, BDD film electrode exhibited fast heterogeneous electron transfer in both internal Fe(CN)6−3/−4 and external Ru(NH3)6+2/+3 redox systems. Under the optimal parameter setting, the maximum signal response of BDD electrode at 40 ‰ was 69 mA/cm2 and the measurement error was less than 0.81 ‰. Appropriate proportion of sp2-C and B-sp3-C phases can significantly improve the detection performance of BDD electrode.

DFT calculations and experiments of oxidation resistance research on B, N, and Si multi-doped diamond films

The oxidation resistance of diamond films is essential in maintaining their good performance in high-temperature applications. Although numerous experiments have proved that doping can improve diamond films' oxidation resistance properties, the theoretical explanation still needs to be discussed. In this study, the density functional theory (DFT) method is used to elucidate the influence mechanism of multiple doping, including B, N, and Si elements doping, on the oxidation resistance of diamond films and obtain the doped diamond films with the optimal oxidation resistance. These include the confirmation of the different doped diamond (111) models, the adsorption site of the O atoms on the various doped diamond surfaces, and the subsequent reaction process of O2 molecules with the C atom. The results show that the multi-doped diamond model has the most considerable activation energy due to the synergistic effect of the three elements, which represents better oxidation resistance properties. In addition, eight kinds of diamond films are fabricated on the silicon substrate. Their weight loss at high temperatures is conducted to evaluate oxidation resistance, indicating that multiple doping can effectively reduce the high-temperature oxidation rate of diamond films, and the experimental results are consistent with the theoretical calculations.

New chemical pathway for large-area deposition of doped diamond films by linear antenna microwave plasma chemical vapor deposition

Today, boron-doped diamond (BDD) is among the key materials for electrochemical sensing and advanced oxidation of micropollutants. Therefore, a cost-effective fabrication of large-area BDD electrodes is of high interest. We present an implementation of a liquid-phase boron precursor trimethyl borate for large-area deposition of boron-doped diamond films by linear antenna microwave plasma CVD. Trimethyl borate vapors were used not only as a source of boron for doping but also as the only source of carbon and oxygen, while completely saturating the requirements for the growth of high-quality boron-doped diamond films. However, to allow for control over the doping level through maintaining the B/C and B/O ratios, carbon dioxide was employed as an additional source of carbon and oxygen. The film morphology was controllable from microcrystalline to ultra-nanocrystalline by changing the concentrations of trimethyl borate. Using this unique precursor system, we were able to grow diamond films with a doping level in range from 8 × 1017 cm−3 to 2 × 1022 cm−3 and resistivity as low as 1.16 × 10−2 Ω·cm. Low activation energies were calculated from the Arrhenius plot and growth rates as high as up to 170 nm/h for the low pressure microwave plasma CVD were reached. The investigation of the plasma emission spectrum revealed a chemical composition similar to that of hydrogen-rich plasmas with methane, and the proposed chemical reactions indicate that the diamond growth takes place via the hydroxyl radical. The results demonstrated that trimethyl borate is a suitable source of carbon and boron for the large-area growth of highly boron-doped diamond via low pressure microwave plasma CVD methods.

Polarized Raman spectroscopy of phosphorous doped diamond films

Polarized Raman measurements were performed on P-doped diamond films to investigate the origin of the peaks in the lower wave numbers, which are unknown to date, and a comparative study of several P-doped substrates was conducted. The measurements with four configurations of the polarized geometries were carried out for five samples with different P and H concentration, [H]/[P] ratios, and film thickness. For four highly P-doped films, several Raman peaks were observed for all four configurations; retaining the Oh7 cubic structure of diamond, presumably relate to substitutional sites. For a sample of high [H]/[P] ratio (=1.17) and a very thick film, several other peaks were observed. The peak appearances for four configurations indicate that the origin is not in the Oh7 diamond structure but presumably interstitial sites. In the future, it may be possible to realize effective P doping by the improvement of film synthesis by utilizing the results of Raman polarization measurements, which are simple and nondestructive.

Electrochemical Semiconductor Analysis By Square Wave Voltammetry

Studies in the past 20 years have utilized cyclic voltammetry (CV) for determining various electronic properties (e.g. density of states, electron carrier concentrations, trap state capacitances) of semiconducting titanium oxide films in photoelectrocatalytic systems such as dye-sensitized solar cells [1-4]. Though primarily used for redox sensing, this work presents square wave voltammetry (SWV) as an alternative to determining said properties. As an electrochemical characterization technique, SWV can provide significantly less background current and greater sensitivity than CV [5]. This is beneficial for the accurate measurement and calculation of electronic properties from electrochemical semiconductor current-voltage data. By varying the applied frequency as well as step and/or pulse sizes of the square wave, one can probe electronic processes of various time scales, in contrast to CV which only allows control of the potential scanning rate across the same potential window [5, 6]. This work presents a comparative study of electronic properties as determined by SWV versus CV for various semiconducting electrodes such as silicon, germanium, titanium oxide, and doped diamond films. This technique was also extended to semiconductor heterostructures - such as noble metal-decorated titanium oxide - for observation of intraband gap states and their contribution to the overall electronic properties of the electrode as determined by SWV.[1] Liu, B. et. al., “Intrinsic intermediate gape states of TiO2 materials and their roles in charge carrier kinetics”, J. Photochem. and Photobio. C: Photochem. Rev., 39 (2019) 1-57[2] Zare, M., Mortezaali, A., and Shafiekhani, A., “Photoelectrochemical determination of shallow and deep trap states of platinum-decorated TiO2 nanotube arrays for photocatalytic applications”, J. Phys. Chem. C, 120 (2016) 9017-9027[3] Fabregat-Santiago, F. et al., “High carrier density and capacitance in TiO2 nanotube arrays induced by electrochemical doping”, J. Am. Chem. Soc., 130 (2008), 11312-11316[4] Abayev, I. et al., “Properties of the electronic density of states in TiO2 nanoparticles surrounded with aqueous electrolyte”, J. Solid State Electrochem, 11 (2007) 647-653[5] Mirceski, V. et al., ”Square-wave voltammetry: A review on the recent progress”, Electroanalysis, 25 (2013) 2411-2422[6] Bard, A. J. and Faulkner, L. R., Electrochemical Methods: Fundamentals and Applications, 2nd ed. Hoboken, NJ: John Wiley & Sons, Inc., 2001.

Structural, Raman and photoluminescence studies on nanocrystalline diamond films: Effects of ammonia in feedstock

Herein, we report on the improvement of structural quality and enhancement of photoluminescence (PL) emission for an optimally N doped nanocrystalline diamond (NCD) film. Pure and N doped nanocrystalline diamond films are synthesized on Si by hot filament chemical vapour deposition using NH3:CH4:H2 at different nominal N/C ratios viz. 0, 0.13, 0.35, 0.50 and 0.75 in feedstock. X-ray diffraction analysis reveal a systematic initial increase and then a decrease in crystallite size with N/C ratio in feedstock. Further, a monotonic increase in Raman line width and peak position of diamond band indicates that the compressive strain in diamond lattice increases as a function of N/C ratio upto 0.50. However, at higher N/C ratio of 0.75, the compressive strain gets relaxed a little and produces a lower strain. Furthermore, a unique Raman mode at 1195 cm−1 is observed corresponding to the C=N-H vibrations indicating a significant N concentration in the NCD films. In addition, visible and UV PL studies reveal the presence of several N-related color centres with multiple emission lines in the range of 380–700 nm. An optimally N doped diamond film grown at N/C ratio of 0.35 in feedstock shows a significant enhancement in room temperature PL emission at ~505 and 700 nm. This PL enhancement is attributed to H3 and other aggregates of N related defect centres, under 355 and 532 nm laser excitations, respectively.

Low temperature synthesis of transparent conductive boron doped diamond films for optoelectronic applications: Role of hydrogen on the electrical properties

Transparent conductive electrodes are principal components in various optoelectronic devices and technologies. As such, diamond coatings in the form of electrically conductive thin films are envisioned to provide advantageous chemical and mechanical characteristics/stability in a variety of modern technologies including optoelectronics, biosensing, electrochemical and micromechanical systems. However, deposition of electrically conductive polycrystalline diamond coatings for such applications is currently a challenging task, since temperatures above 600 °C are usually required to ensure good diamond layer quality, which in turn limits the selection of substrates, to materials capable of withstanding exposure to high temperatures. In the present work, we investigate routes toward enhancement of electrical characteristics of nanocrystalline boron-doped diamond (BDD) films fabricated at low temperatures via chemical vapour deposition. We found that post-growth processing of BDD layers enhances their electrical properties, which otherwise are dependent on the employed deposition temperature regime. Finally, we show that integration of an electrically conductive Ti grid opens a route for fabrication of highly transparent and conductive composite nanocrystalline BDD electrodes over large areas at temperatures as low as 250 °C.

X-ray absorption near edge structure and extended X-ray absorption fine structure studies of P doped (111) diamond

The P dopant site control in diamond is critical to achieve high mobility n type channels and high concentration n+ layers for power device applications. In this study, the P doped diamond films grown by three institutes with varying hydrogen and dopant concentrations were analyzed by X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). By XANES, the film with high H concentration (4.0 × 1019 cm−3) was estimated to show a higher peak intensity of 2147.7 eV than that of a low H concentration film. H was likely to be incorporated in the diamond as P-H at the substitutional sites under H rich growth condition. Another film showed considerably low peak intensities at 2147.7 and 2148.6 eV because of the “substitutional with H” and “substitutional” sites, respectively. The EXAFS result revealed that the first nearest neighbor distance is slightly shifted from the “substitutional” to “interstitial” site. The low P concentration film showed different types of energy profiles, particularly in the high energy region, indicating that dopant sites change with dopant concentration. Overall, the P dopant site is likely to be influenced by the machine system, H and P concentrations.

High temperature tribology of heavily boron doped diamond films against steel

Despite the fact that Fe, Co, and Ni catalyze the phase transition of diamond into graphite, the question of the applicability of diamond as a functional coating of a metal-cutting tool is still open. For this reason, our work contains investigation of wear and friction of heavily boron doped diamond films against steel at elevated temperature, as well as influence of boron concentration on diamond film oxidation resistance. The obtained data indicated that minimum CoF value is achieved in the temperature range within 570–670 °C and strongly depends on boron concentration in coating (CoF decreases with increasing of boron concentration). Wear rate has the same dependence as the CoF, whereas oxidation resistance decreases with increasing of boron concentration. Besides, the presented results are first obtained for boron doped diamond films synthesized under high B/C ratio conditions (of up to 333 ppb).

Annealing temperature regulating the dispersity and composition of nickel-carbon nanoparticles for enhanced glucose sensing

Design of electrodes with both excellent electrocatalytic activity and facile synthesis process is the pivotal challenge in the progress of non-enzymatic glucose sensors. In this work, a series of highly dispersed nickel-carbon nanoparticles modified boron doped diamond composite electrodes were fabricated after the boron doped diamond films with a sputtering nickel layer being annealed at different temperature in hydrogen atmosphere. The surface morphology and interface structure of nickel-carbon nanoparticles modified boron doped diamond samples were characterized detailedly with the increase of annealing temperature. The charge transfer of synthesized electrodes was improved with the increasing content of sp2 carbon and the improvement of crystallinity of nickel. Therefore, the volcano-type electrocatalytic performance trend was observed with the composite electrode prepared after annealing at 500 °C presenting the best glucose sensing performance with the sensitivities of 1730 and 1081 μA cm−2 mM−1 in glucose concentration ranges of 0.01–2.12 and 2.12–9.06 mM respectively and a low detection limit of 0.2 μM (S/N = 3).

The occupied electronic structure of ultrathin boron doped diamond.

Using angle-resolved photoelectron spectroscopy, we compare the electronic band structure of an ultrathin (1.8 nm) δ-layer of boron-doped diamond with a bulk-like boron doped diamond film (3 μm). Surprisingly, the measurements indicate that except for a small change in the effective mass, there is no significant difference between the electronic structure of these samples, irrespective of their physical dimensionality, except for a small modification of the effective mass. While this suggests that, at the current time, it is not possible to fabricate boron-doped diamond structures with quantum properties, it also means that nanoscale boron doped diamond structures can be fabricated which retain the classical electronic properties of bulk-doped diamond, without a need to consider the influence of quantum confinement.

Study of self-masking nanostructuring of boron doped diamond films by RF plasma etching

The surface nanostructuring of boron doped diamond (BDD) can further enhance its unique properties e.g. in electrochemical sensing, photoelectrochemical cells, field emission devices and various kinds of sensors. Here we present an investigation of plasmatic nanostructuring of BDD films without use of a time-consuming masking process. RF plasma technique was used to etch surface nanostructures with dimensions ranging from tenths to hundreds of nm in width and height. The size and shape of achieved diamond nanostructures were influenced only by applied etching parameters. We have found that the etched carbon is re-deposited in an amorphous form creating a mask and this self-masking process is responsible for the final shape of obtained structures.Therefore, this technique is effectively controllable by changing plasma power, gas type and pressure which influence the energy of incident ions and thus the sputtering yield and re-deposition of masking material. Utilization of various gas types, pressures and RF powers revealed the physical type of etching to be dominant over the chemical at both high and low energy ions. The nanostructured surfaces were then observed and characterized by SEM and Raman spectroscopy to investigate the nanostructures dimensions and to confirm the remaining diamond quality.

Charging effects and anomalous resistive features of superconducting boron doped diamond films

Anomalous resistive peaks below the superconducting transition temperature in heavily boron doped nanocrystalline diamond films could have potential application in switching devices, however it’s exact origin is still under study. We establish a temperature dependence of this resistive phase similar to what has been reported for in Josephson junction arrays and other granular superconductors where the charge duel of the Berezinskii-Kosterlitz-Thouless (BKT) transition has been observed. Non-linear magnetic field dependence of the resistance with a temperature dependent peak feature below the critical field are also presented. Pronounced temperature dependent hysteresis in the current voltage sweeps at temperatures below the determined BKT critical point are related to pinning of charge defects. It is shown that these collective features allude to a Charge-BKT transition between charge and anti-charge analogues.

Phosphorus-doped (113) CVD diamond: A breakthrough towards bipolar diamond devices

Among wide bandgap semiconductors, diamond presents physical properties particularly suited for high performance power electronic devices. Growth and doping of chemical vapor deposited (CVD) diamond have been mainly optimized in the conventional (100) crystal orientation, highly studied on (111) surfaces and recently initiated on (113). This last orientation seems very promising, as is shown for intrinsic and p-type doped diamonds. In this work, we report the growth of CVD phosphorus doped diamond films on (113)-oriented substrates. The (113) homoepitaxial layers present a phosphorus content in the range of 7.2 × 1016 up to 4.5 × 1019 at/cm3 for thicknesses between 0.6 μm and 4 μm. The high quality and the full incorporation of phosphorus into donor sites found for the (113) crystal orientation open new architecture possibilities for bipolar diamond devices.

Characterisation of thin boron-doped diamond films using Raman spectroscopy and chemometrics

A non-destructive chemometric method to determine thickness and boron concentration of as-deposited, thin, heavily doped diamond films by Raman microscopy.

BDD-Electrolysis of Oxalic Acid in Diluted Acidic Solutions

Boron doped diamond films (BDD) are the most studied electrocatalytic materials and their efficiency for removing organic compounds is attributed to their ability to produce a large amount of hydroxyl radicals by the electrolysis of water. However, some organic compounds are easy to degrade than others, as well as they also interact with BDD surface. Thus, it is necessary to understand the chemical/electrochemical process at the molecular level. In this frame, this work aims to study the electrochemical oxidation (EO) of oxalic acid (OA) at BDD anode, understanding the reaction mechanism, formation of hydroxyl radicals, the effect of supporting electrolyte concentration, and the role of oxidants in solution taking into consideration the cyclic and linear voltammetric measurements. Voltammetric results clearly reveal that a direct electron transfer is achieved as the main mechanistic behavior suffered by OA on BDD surface before oxygen reaction. However, the concentration of sulfates in solution plays an important role in the solvation, diffusion and adsorption species at BDD surface, promoting parallel mechanisms. From the information provided by experimental measurements, the preferential mechanism on BDD surface at low or high overpotential regions was elucidated.

"Surface Roughness and Seeding Process Influence on Boron Doped Micro/Nanocrystalline Diamond Adhesion on Titanium Substrate"

CVD (Chemical Vapor Deposition) diamond deposition on different materials requires surface treatment such as diamond particles seeding on the substrate dispersed in an appropriate solvent by using ultrasonic agitation. On the other hand, seeding process by electrostatic attraction of nanodiamond particle have produced films with higher nucleation density compared to that obtained from ultrasonic treatment. In addition, nucleation and growth of micro/nanocrystalline boron doped diamond films (BDD/NBDD) on titanium (Ti) substrates represent a complex process, mainly due to the poor film adhesion related to the difference in the thermal expansion coefficients between the film and the substrate.