Boron-doped Diamond-like Carbon Research Articles

The development of B/Cr co-doped DLC coating by FCVA deposition system and its tribological properties at 300 °C

The diamond-like carbon (DLC) coating prepared using filtered cathodic arc deposition (FCVA) lost its promising wear resistance under high temperatures. Element-doped DLC coatings have been investigated to suppress carbon oxidation reaction and subsequently enhance the wear resistance in high-temperature environments. Previous research clarified the excellent tribological properties of boron-doped DLC (B-DLC) but identified challenge such as arc discharge extinguishment and coating declamation (under high-temperature friction test). In this study, the introduction of Argon gas (10 sccm) during the deposition process stabilized stable arc discharge, resulting in high hardness and deposition rate. Moreover, a chromium interlayer and varying concentration of Cr dopant (0.5 %, 1.0 %, 3.0 % at.) were added to B-DLC to develop a stable, co-doped DLC with low friction and high wear resistance. Raman spectroscopy and nano-indentation revealed an increase in the disordered carbon structure and reduction in hardness and Young's Modulus with Cr doping. Macroscopic ball-on-disk friction test, showed 1 % Cr-doped B-DLC (a-C:B:Cr1) coating exhibited super low friction (avg. coefficient 0.02) and a low specific wear rate (<5.0 × 10−6 mm3/Nm). Raman spectroscopy indicated that the transferred graphite-like tribo-film onto the surface of Si3N4 counterparts contributed to stable low friction. Additionally, XPS analysis on the DLC coatings' wear track suggested the rich BB bond might contribute to its high wear resistance. This successful improvement on element-doped DLC prepared by FCVA provided valuable insights for further exploration of DLC coating applied to various working situations.

Growth of boron-doped diamond-like carbon films from a low-pressure high-density plasma in inductively coupled chemical vapour deposition

The main objective of this work was the preparation and optimization of boron-doped diamond-like carbon (DLC) films having a good crystalline structure, and electronic and optical properties, at an extremely low deposition pressure and relatively low growth temperature, by varying the flow rates of precursor gases (CH4, B2H6, and Ar) in the plasma controlled at 800 W of RF power. Planar inductively coupled plasma-enhanced chemical vapour deposition technique was used to enable deposition at ∼5.33 Pa and 450 °C, at a constant negative substrate bias of -40 V. The flow rate of the dopant gas (B2H6) was changed to obtain a set of samples, while the precursor gas (CH4) flow rate was kept fixed. The doped sample, prepared with B2H6/CH4 ratio (r) = 1 %, was found to possess a maximum ID/IG (intensity ratio of the D peak with the G peak) of ∼0.819 and a minimum IDia/IG ratio (relative intensity of the Diamond peak to the G peak) of ∼1.149. A high sp3 content of ∼50 % was revealed from the X-ray photoelectron spectroscopy analysis and the transmission electron microscopy images also indicated the presence of prominent 〈111〉, 〈220〉, and 〈311〉 crystallographic planes. The B-doped DLC film possessed enhanced electrical conductivity (σRT) of ∼3.02 ×10−5 S cm−1 relative to the intrinsic DLC films, a corresponding minimum of activation energy (ΔEH) (as calculated in the above room-temperature regime) of ∼170 meV, an optical band gap (Eg) of ∼3.35 eV, and the root mean square roughness of ∼48.12 nm.

Preparation of boron-doped diamond-like carbon films via enhanced-PECVD using an additional cathode

Boron-doped Diamond-Like Carbon (B:DLC) films with different concentrations of boron were produced in an Enhanced-PECVD reactor using trimethylborate (TMB) vapor as the boron source. An additional cathode system was incorporated inside the reactor to confine the plasma to grow B:DLC film on polished Ti-6Al-4 V and Silicon samples. The boron-containing coatings were evaluated and compared to a boron-free coating through several characterization techniques. Raman spectroscopy, Nano-hardness, XPS, RBS, and SEM techniques were employed to study the microstructure, hardness, chemical composition and bonding state, and morphology of the samples. Ball-on-disc tests were also conducted, using a tribometer to measure the friction coefficient and wear resistance. Boron was confirmed in the DLC film structure by XPS and RBS analyses. The XPS measurements showed that the boron bonding was accompanied by a higher content oxygen than carbon content, which increased with the TMB concentration. The sp3 content was evaluated, and the result showed a decrease of about 30 % with the higher solution concentration. As a consequence, the friction coefficient, wear, and hardness were affected. However, the adherence of the films was not compromised. Finally, our study indicated that the PECVD deposition system employing an additional cathode was suitable for the incorporation of boron into DLC films.

Tribological performance of 52,100 steel subjected to boron-doped DLC coating and ultrasonic nanocrystal surface modification

The tribological performance of AISI 52100 substrates subjected to several surface treatments have been evaluated in rolling, sliding, and mixed mode contact. The surface treatments include a boron-doped diamond-like carbon (B-DLC) coating deposited by plasma-assisted magnetron sputtering, an ultrasonic nanocrystal surface modification (UNSM) technique used to generate severe plastic deformation in the near surface of the steel specimens, and a B-DLC coating applied to a UNSM pretreated surface. In general, the tribological performance of the duplex surface treatment was superior to that of the untreated specimens and of the specimens with the other surface treatments in rolling, sliding, and mixed mode contact. The improved tribological performance of the duplex process was attributed to the combination of increased wear resistance provided by the B-DLC coating and the grain refinement of the martensitic structure of the AISI 52100 imparted by the UNSM process that created a beneficial substrate/coating interface.

Improved Thermal Resistance and Electrical Conductivity of a Boron-Doped DLC Film Using RF-PECVD

Diamond-like carbon (DLC) film doped with boron has unique properties and displays higher thermal resistance, lower internal stress, and better electrical conductivity than un-doped DLC film; this makes it is suitable for various applications, especially in outer space. Radio-frequency plasma-enhanced chemical vacuum deposition of boron-doped DLC film was performed to determine the optimal percentage of boron for improving thermal resistance. Additional heat treatment and 40% B2H6/CH4 yielded the best electrical conductivity. X-ray photoelectron spectroscopy, thermal gravimetric analysis, Raman spectroscopy, and the four-point probe method were utilized to analyze the properties of boron-doped DLC film. The boron-doped DLC film displayed outstanding performance in terms of thermal resistance and electrical conductivity.

Adsorption properties of molybdenum based FMs on boron-doped DLC

Development of low friction surface materials matched with low friction lubricants is an important route to improving engine efficiency and reducing emissions. Diamond-like carbon (DLC) is a material of interest because it combines the durability of diamond with the low friction properties of graphite. Consequently, various forms of DLC have been studied as durable, low friction surface coatings. At the same time, friction modifiers (FMs) are often used in engine lubricants to produce low friction surface layers. Molybdenum-based friction modifiers are commonly used additives that mechanochemically decompose to cover surfaces with MoS2, a solid lubricant. FMs can also reduce friction on DLC surfaces. However, molybdenum can be harmful to DLC and cause rapid degradation and breakthrough of the DLC surface layer. We have found that the wear debit of molybdenum FMs trends with surface affinity of the additive. The adsorption isotherms of 4 Mo-based FMs on boron-doped diamond-like carbon (BDLC) were measured with a quartz crystal microbalance (QCM). The strongest adsorbate, Mo dithiophosphate (MoDTP), which also forms the thickest film, protects the BDLC surface enabling low friction while keeping wear low. Theoretical predictions based on molecular dynamics simulations combined with molecular-thermodynamic theory (MD-MTT) show that adsorption of MoDTP on BDLC deviates significantly from Langmuir behavior and free energy of adsorption for the first monolayer is significantly more negative than the multilayer adsorption free energy observed experimentally. The relationship between wear and adsorption behavior is consistent with experimental observations in the literature. These results also suggest that additive performance in a fully formulated lubricant is related to fundamental adsorption properties measured on the neat additive.

Optical and electrical properties of synthesized reactive rf sputter deposited boron-rich and boron-doped diamond-like carbon thin films

Boron-doped diamond-like carbon (B-DLC) and boron-rich DLC thin films have been deposited on n-type silicon and quartz substrates by reactive rf magnetron sputtering process. Boron carbide (B4C) target was used in the deposition. Reducing the boron/carbon ratio was achieved by either using hydrogen gas or by introducing a proper flow rate of methane. Another approach of producing B-DLC thin films was achieved by using low methane\argon ratio (5/40) while sputtering atoms from non-saturated target-surface under various sputtering rf powers. The maximum film graphitization and lowest band gap energy was achieved by applying 100 W power. The Auger electron spectroscopy and Raman shifts were used to investigate the composition of the films. The optical properties were investigated using spectroscopic ellipsometry and spectrophotometer. Furthermore, p-type B-DLC/n-type Si(100) heterojunction diode was fabricated and the I–V characteristics were investigated against the flow rates of methane or the rf power.

Development of High-Sensitive Detection System for Redox Analytes Having a Standard Potential Higher Than O2 Evolution by Using Micropatterned Conductive Boron-Doped DLC Electrodes

1. Introduction Recently, cobalt, manganese and cerium are widely used in mass-produced products such as a lithium ion battery. It has been reported that the excessive consumption of these metal ions causes various diseases like neurotoxicity. In industrial wastewater discharge standards, Co2+, Mn2+ and Ce3+contents of wastewater has been regulated below several micro-molar. These redox species are generally analyzed using photochemical method. Some time, however, is required for analysis using the method and initial measures cannot be taken promptly when problems such as the content of metal ions exceeding the discharge standard occur. Therefore, electrochemical monitoring system which can shorten time of analysis should be developed. The standard potential of Co2+, Mn2+ and Ce3+ are higher than that of O2evolution potential. Redox reactions of these analytes cannot be observed at conventional metal electrodes. In this study, boron-doped diamond-like carbon (B-DLC) [1] with higher overpotential for O2evolution was selected as the electrode that redox reaction of the analytes can be observed. The detection limit of Ce3+ (model analyte) at a flat-disk electrode of B-DLC was 39 mM. Our research group tried to fabricate interdigitated microarray electrodes (IDA) because it shows one or two orders of magnitude higher sensitivity than that of the flat-disk electrode. IDA are composed of two sets of microband array neighbored (called generator and collector). The potential of one microband pairs (collector) is set at reduction potential of redox analyte, and that of the other is swept toward oxidation potential (dual mode). Redox cycling occurs between two sets of the microband pairs. The generator exhibits higher amplification of oxidation current by redox cycling compared to the current without applying the potential on the collector (single mode). We have reported that B-DLC-IDA with 2 mm/2 mm of bandwidth/gap exhibited ca.10 times amplification factor corresponding to the theoretical value [2]. The amplification factor of Ce3+, however, was half of the theoretical value. As a result, the detection limit was 8.8 mM. The reduction of Ce4+ is not promoted at the collector because the sample solution is a reductant. Moreover, Ce3+generated at the collector is hardly supplied to generator by diffusion, which causes inefficient redox cycling. When the collector is set at an oxidation potential, Ce3+ are constantly supplied to the collector by nonplanar diffusion. Ce4+generated at the collector is considered to be supplied to the generator at a higher diffusion rate. In this report, amplification factor of Ce3+was tried to be improved by changing the potential set at the collector. 2. Experimental B-DLC was synthesized on quartz substrates with RF plasma CVD method using a mixed solution of n-hexane and trimethyl borate as a source material. RF power was 175 W and the deposition time was 40 minutes. The alminium pattern of IDA was fabricated by the lift-off technique using photoresist and alminium deposition. Alminium on B-DLC-IDA was removed in a sodium hydroxide solution after O2plasma etching of B-DLC. The structure of B-DLC-IDA was designed to be 65 pairs of microbands with a length of 200 μm and bandwidth/gap of 2.0 mm. Single-dual mode measurements were carried out using the B-DLC-IDA in 1 mM Ce(NO3)3 + 0.1 M HNO3solution. 3. Results and discussion Figure1 shows the optical micrographs of the B-DLC-IDA. The bandwidths and gaps were observed to be 1.96 and 2.04 mm, respectively. The deviation between the actual gap and the designed value was less than 2%. Raman spectra of B-DLC were identical before and after the processing of IDA. It was confirmed that amorphous structure and composition ratio of sp2/sp2+sp3 (= 75%) in B-DLC did not change during IDA processing. The working potential range in 0.1 M sulfuric acid was constant after IDA processing. These results suggest that the redox reaction of Ce3+can be served at the B-DLC-IDA. In the dual mode of Ce3+, the potential of the collector was set at 1.37 V, and the potential of generator was swept from 0.8 to 1.7 V. Amplification factor closed to the theoretical value could be obtained. The detection limit of Ce3+was decreased from 8.8 to 4.4 mM by changing the applied potential of the collector from 1.25 to 1.37 V. 4. Summary Fabrication of the B-DLC-IDA and optimizing method of electrochemical measurement can establish highly sensitive electrochemical system that can analyze redox species with a standard potential higher than O2evolution. 5.

Characterization of boron doped diamond-like carbon film by HRTEM

Boron doped diamond-like carbon (B-DLC) film was synthesized on silicon (100) wafer by biased target ion beam deposition. High-resolution transmission electron microscopy (HRTEM) is employed to investigate the microstructure of the B-DLC thin film in cross-sectional observation. Many crystalline nanoparticles randomly dispersed and embedded in the amorphous matrix film are observed. Through chemical compositional analysis of the B-DLC film, some amount of O element is confirmed to be contained. And also, some nanoparticles with near zone axes are indexed, which are accordance with B2O phase. Therefore, the contained O element causing the B element oxidized is proposed, resulting in the formation of the nanoparticles. Our work indicates that in the B-DLC film a significant amount of the doped B element exists as boron suboxide nanoparticles.

Electrochemical performances of B doped and undoped diamond-like carbon (DLC) films deposited by femtosecond pulsed laser ablation for heavy metal detection using square wave anodic stripping voltammetric (SWASV) technique

Pure diamond-like carbon (DLC) thin films and boron-doped DLC thin films have been deposited on silicon substrates using femtosecond pulsed laser. The amorphous carbon materials (DLC), have been deposited at room temperature by ablating graphite targets with an amplified Ti:sapphire laser of 800 nm wavelength and a pulse duration of 150 fs in high vacuum conditions. Doping with boron has been performed by ablating alternatively graphite and boron targets. In this study, the DLC films were used as working electrodes for the electrochemical detection of trace heavy metals namely, Cd 2+, Pb 2+, Ni 2+ and Hg 2+, by using square wave anodic stripping voltammetry (SWASV) technique. Four metals were detected at −1.3 V deposition potential, and 90 s deposition time. The DLC films have been characterized by multiwavelength Raman spectrometry and high resolution scanning electron microscopy. The effect of the boron doping on the electrochemical behavior has been shown. The a-C:B 8%/Si 3N 4 electrode gives the more sensitive detection. The four metals are detected simultaneously with a detection limit of 1 μg/L or 2 μg/L and a dynamic range from 1 or 2 to 25 μg/L for every metal, as presented in third table of this article. The different sensitivities obtained are 6.2, 20.0, 1.2 and 6.6 μA/ppb or μA μg −1 L for Cd 2+, Pb 2+, Ni 2+ and Hg 2+, respectively.

Characterization of boron-doped diamond-like carbon prepared by radio frequency sputtering

Instead of the sophisticated deposition processes and boron sources reported in literature, the study used the radio frequency magnetron sputtering method to prepare boron-doped diamond-like carbon (DLC) films with p-type conduction. The adopted sputtering targets were composed of boron pellets buried in a graphite disc. The undoped DLC films prepared exhibited n-type conduction, based on the Hall-effect measurement. For boron content ≥ 2.51 at.%, the films showed semiconductor behavior converted from n-type to p-type conduction after annealing at 450 °C. B-DLC films with a boron content of 5.91 at.% showed a maximum carrier concentration of 1.2 × 10 19 cm −3, a mobility of 0.4 cm 2/V s, and an electrical resistivity of 1.8 Ω cm. The results of XPS and Raman spectra indicated that the motion of boron atoms was thermally activated during post-annealing, helping promote the formation of C–B bonds in the films. Moreover, the doping of boron in DLC films decreased sp 3 bonding and facilitated carbon atoms to form sp 2 bonding and graphitization.

Electrical properties of boron-doped diamond-like carbon thin films deposited by femtosecond pulsed laser ablation

We report on electrical measurements and structural characterization performed on boron-doped diamond-like carbon thin films deposited by femtosecond pulsed laser deposition. The resistance has been measured between 77 and 300 K using four probe technique on platinum contacts for different boron doping. Different behaviours of the resistance versus temperature have been evidenced between pure DLC and boron-doped DLC. The a-C:B thin film resistances exhibit Mott variable range hopping signature with temperature. Potential applications of DLC thin films to highly sensitive resistive thermometry is going to be discussed.

Diamond-like carbon (DLC) microelectrode for electrochemical ELISA

A diamond-like carbon (DLC) microelectrode was applied to commercial ELISA kits for medical diagnosis of HIV (human immunodeficiency virus), HBV (human hepatitis B virus), HCV (human hepatitis C virus). In this work, quantification of oxidized 3,3′,5,5′-tetramethylbenzidine (TMB) was carried out by using a microelectrode made of boron-doped DLC and cyclic voltammetric analysis method without the conventional quenching step which uses sulfuric acid. The microelectrode provided well-known step-shaped graphs, and limit of detection could be improved by clear determination of electrochemical oxidative and reductive peaks. To demonstrate the applicability of DLC microelectrode to conventional ELISA kits, commercial ELISA kits for detection of HIV antigen, HBV antigen and HCV antigen were also tested. These results proved that the applicability of DLC microelectrode to practical detection is feasible.

Characterization of phosphorus-doped and boron-doped diamond-like carbon emitter arrays

We synthesized phosphorus-doped and boron-doped emitters by using trimethylphosphite P(OCH3)3 and trimethylborate B(OCH3)3 as doping sources in a microwave plasma chemical vapor deposition system. Based on our experimental results from scanning electron microscopy and Raman spectra, there is much difference among undoped, phosphorus-doped, and boron-doped diamondlike material. In addition, doping both phosphorus and boron can enhance electric properties by reducing the turn-on voltage and can increase the emission current density. The turn-on voltages of undoped, boron-doped, and phosphorus-doped emitters in triode-type field emitter arrays are 15, 8, and 5 V, respectively. The emission currents of boron-doped and phosphorus-doped emitters are about 20 and 80 times larger than the undoped.

Boron-doped diamond-like amorphous carbon as photovoltaic films in solar cell

In this paper, the photovoltaic feature of metal-boron carbide-silicon (MCS) solar cell was reported. The boron-doped diamond-like carbon thin film on n-silicon substrate has been prepared using arc-discharge plasma chemical vapor deposition (PCVD) technique. The conductivity and the resistivity of the film were measured by Bio-Rad Hall5500PC system to be p-type semiconductor and 3–12 Ω cm/□, respectively. The boron content in the films was about 0.8–1.2%, obtained from Auger electron spectroscopy (AES), and some microcrystalline diamond grains (0.5–1.0 μm) embedded in the mainly amorphous network were revealed through scanning electron microscope (SEM) and Raman spectrum. The performance of Au/C(B)/n-Si heterojunction solar cells has been given under dark I– V rectifying curve and I– V working curve (with 100 mW cm −2 illumination). A measurement of open-circuit voltage V oc=580 mV and short-circuit current density J sc=32.5 mA cm −2 was obtained. Accordingly, the energy conversion efficiency of the device was tentatively determined to be about 7.9% in AM 1.5, 100 mW/cm 2 illuminated.

Electron Field Emission Characteristics of Planar Field Emission Array with Diamondlike Carbon Electron Emitters

The electron emission characteristics of planar field emission arrays (FEAs), containing undoped and boron-doped diamondlike carbon (DLC) films as emitters, were investigated. The planar DLC FEAs require only 13.3 V/µm to turn on the electron field emission, whereas the boron-doped planar DLC FEAs requires an even lower electric field (9.8 V/µm) to trigger the electron emission. The boron-doped DLC films also possess an electron emission property highly superior to that of the undoped DLC films and exhibit a stable electron emission current of 938 µA under a 20 V/µm bias voltage, which corresponds to a high emission current density of (Je)B-DLC=128 mA/cm2. These superior properties suggest that the boron-doped DLC FEAs are potentially useful as electron emitters in flat panel displays.

Rhodium and iridium as deep impurities in silicon : K. P. Lisiak and A. G. Milnes. Solid State Electronics19, 115 (1976)

In this paper, the photovoltaic feature of metal-boron carbide-silicon (MCS) solar cell was reported. The boron-doped diamond-like carbon thin film on n-silicon substrate has been prepared using arc-discharge plasma chemical vapor deposition (PCVD) technique. The conductivity and the resistivity of the film were measured by Bio-Rad Hall5500PC system to be p-type semiconductor and 3–12 Ω cm/□, respectively. The boron content in the films was about 0.8–1.2%, obtained from Auger electron spectroscopy (AES), and some microcrystalline diamond grains (0.5–1.0 μm) embedded in the mainly amorphous network were revealed through scanning electron microscope (SEM) and Raman spectrum. The performance of Au/C(B)/n-Si heterojunction solar cells has been given under dark I–V rectifying curve and I–V working curve (with 100 mW cm−2 illumination). A measurement of open-circuit voltage Voc=580 mV and short-circuit current density Jsc=32.5 mA cm−2 was obtained. Accordingly, the energy conversion efficiency of the device was tentatively determined to be about 7.9% in AM 1.5, 100 mW/cm2 illuminated.