Doped Diamond Films Research Articles

The spatial inhomogeneity and X-ray absorption spectroscopy of superconducting nanocrystalline boron doped diamond films

The local electrical conductivity and impurity band evolution in superconducting nanocrystalline boron doped diamond (BNCD) film are investigated using conducting atomic force microscopy (C-AFM) and X-ray absorption spectroscopy (XAS). C-AFM has been employed to investigate the local conductivity of superconducting BNCD with Tc = 4.3 K and upper critical field Hc2(0) = 5.2 T. A high local electrical heterogeneity of the BNCD film as evidenced from the C-AFM profile points to the uneven boron uptake during the process of doping. C-AFM also revealed that grain boundaries are the highly conducting regions, possibly, due to the presence of p-type trans-polyacetylene along with the CC and CH bonds in the grain boundaries. From the in-depth XPS profiling of the B 1s spectra we confirmed the macroscopic uniformity of the boron concentration across the depth of BNCD layers. X-ray absorption spectroscopy (XAS) measurements near B K-edge and C K-edge showed formation of in-gap states as a result of heavy boron doping. Near C K-edge, bandgap states at 282.8 eV and 284.1 eV are found which are responsible for superconductivity in the BNCD film. This work explores the non-uniform boron doping and its effect on the conduction band structure of a superconducting BNCD film.

The optimization of the doping level of boron, silicon and nitrogen doped diamond film on Co-cemented tungsten carbide inserts

Boron doped, silicon doped and nitrogen doped diamond films with different doping level in gas phase are deposited on Co-cemented tungsten carbide (WC-Co) inserts using hot filament chemical vapor deposition (HFCVD) method. Trimethyl borate ((CH3O)3B), tetraethoxysilane (Si(OC2H5)4) and urea (CO(NH2)2) are dissolved in acetone to serve as boron, silicon and nitrogen precursors, respectively. The as-deposited diamond films are characterized by field emission scanning electron microscope (FESEM), Raman spectroscopy and indentation tests. The results suggested that doping source and doping level will affect the surface morphology, growth rate, quality and adhesion of diamond film. The optimized doping level to obtain diamond films deposited on WC-Co substrate for mechanical applications with well faceted crystal, low defect, low cluster structure and high adhesive strength is 5000 ppm, 10000 ppm and 10000 ppm for boron, silicon and nitrogen doping, respectively.

Enhancement in conductivity of boron doped diamond films deposited by the methanol/acetone/B2O3 system

The gaseous boron sources such as trimethylboron and borane have been wildly used for boron-doping of diamond film with a high conductivity. Methanol and acetone/B2O3/CH4 (C-B with CH4) has also been selected as a doping system for its low cost. But the resulting boron-doped diamond (BDD) film exhibited a lower conductivity. The BDD film was deposited by the system of methanol and acetone/B2O3 without CH4 (C-B) and exhibited a higher conductivity and larger carrier concentration. It is found that oxygen plays an important role during the deposition. A large number of vacancies for boron filling can be generated in the diamond film from the CO bonds. The addition of CH4 decreased the number of oxygen atoms so that fewer vacancies occurred. Enhancement in conductivity results from more boron atoms in the diamond film using the mixed methanol/acetone/B2O3 system.

Chemical modification of diamond surface by a donor–acceptor organic chromophore (P1): Optimization of surface chemistry and electronic properties of diamond

The first systematic study of P1-dye attachment to the surface of H-terminated boron-doped diamond (BDD) surface was carried out. Details about surface anchoring chemistry were explored on model nanodiamond particles. The electronic properties of boron doped diamond films were tuned from semiconducting to quasi-metallic ones. The relevant materials were analyzed by advanced chemical analysis, zeta-potential, IR and TEM (nanoparticles), Raman, XPS, AFM, SEM, Hall-effect and by in-depth photo/electrochemical studies (films). An improved photochemical grafting protocol was developed leading to a factor of 3 enhancement in photocurrent on comparable diamond electrodes. The champion electrode provided at 1 sun illumination a photocurrent of 6.6μAcm−2 which is the best value ever reported for a flat BDD electrode.

Flux pinning and improved critical current density in superconducting boron doped diamond films

The ability to carry transport current in a magnetic field is the most important aspect of a superconductor. We present a detailed analysis of the upper critical field (Hc2(0)) and vortex dynamics in superconducting boron doped diamond (BDD) films. Hc2(0) measured on the samples of different doping levels revealed a high critical field of up to 7.3 T. Pinning potential U0, estimated using thermally activated flux-flow (TAFF) model shows that U0 is of the order of 102 K. Self-field critical current density (Jc) estimated for the superconducting BDD films showed large Jc ∼ 107 A/cm2 due to enhanced flux trapping.

Synthesis, Characterization of Elastic and Electrical Properties of Diamond-like BCx Nano-Phases Synthesized under High and Low Pressures

ABSTRACTThis paper presents experimental results on the synthesis of boron rich diamond-like carbon phases (BCx) obtained by high pressure sintering (s-BCx) and pulsed laser deposition (PLD-BCx). It has been shown that sintering of a mixture of a powder of micro-diamonds with a powder of boron in the toroid type high pressure device leads to the creation of s-BCx phase with a low resistivity, and high elastic moduli. The PLD-BCx film found to be rigid with the resistivity as low as that of best conductive boron–doped diamond films. It indicates that the presence of B atoms in a laser plasma leads to the formation of sp3 bonds in the material in the process of chemical sputtering. The combination of unique characteristics can be achieved by changing the ratio B/C.

Evaluation of Fatigue Properties of Boron Doped Diamond Film Synthesized on WC-Co Alloy

Evaluation of Fatigue Properties of Boron Doped Diamond Film Synthesized on WC-Co Alloy

Electrical current at micro-/macro-scale of undoped and nitrogen-doped MWPECVD diamond films

Chemical, structural, morphological and micro-/macro-electrical properties of undoped and nitrogen-(N-)doped diamond films are determined by X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, field emission scanning electron microscopy, atomic force microscopy, scanning capacitance microscopy (SCM) and two points technique for I–V characteristics, respectively. The characterization results are very useful to examine and understand the relationship among these properties.The effect of the nitrogen incorporation in diamond films is investigated through the evolution of the chemical, structural, morphological and topographical features and of the electrical behavior. The distribution of the electrical current is first assessed at millimeter scale on the surface of diamond films and then at micrometer scale on small regions in order to establish the sites where the carriers preferentially move. Specifically, the SCM images indicate a non-uniform distribution of carriers on the morphological structures mainly located along the grain boundaries.A good agreement is found by comparing the electrical currents at the micro- and macro-scale. This work aims to highlight phenomena such as photo- and thermionic emission from N-doped diamond useful for microelectronic engineering.

Effect of boron doping on first-order Raman scattering in superconducting boron doped diamond films

Aggregation of impurity levels into an impurity band in heavily boron doped diamond results in a background continuum and discrete zone centre phonon interference during the inelastic light scattering process. In order to understand the Raman scattering effect in granular BDD films, systematically heavily doped samples in the semiconducting and superconducting regimes have been studied using the excitation wavelengths in the UV and visible regions. A comprehensive analysis of the Fano resonance effect as a function of the impurity concentrations and the excitation frequencies is presented. Various Raman modes available in BDD including signals from the grain boundaries are discussed.

Theoretical Model of the Stripline Measurement Cell for Doped Diamond Films

A method for measurement of electrophysical properties of delta-doped diamond samples loaded into the measurement cell based on symmetrical stripline is demonstrated. The simulation of S-parameters of the measurement cell with doped diamond samples is carried out. The influence of the carrier density on the transmission characteristics of the symmetric stripline with doped diamond film is investigated. An increase of the carrier density in the doped diamond film from 5·1019 m-3 to 1022 m-3 leads to frequency shift of transmission characteristic minimum from 15.85 GHz to 16 GHz and increasing of incretion losses from -15 dB to -25 dB.

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.

The use of thin diamond films in fiber-optic low-coherence interferometers

In this paper we present the use of thin diamond films in fiber-optic low-coherence interferometers. Two kinds of diamond surfaces were used: undoped diamond film and boron- doped diamond film. They were deposited on glass plates as well as silicon layers. A conventionally used mirror was used as a reference layer. Diamond films were deposited using Microwave Plasma Enhanced Chemical Vapour Deposition (μPE CVD) system. Measurements were performed using two superluminescent diodes (SLD) with wavelengths of 1300 mm and 1550 mm. The optimal conditions for each layers were examined: the required wavelength of the light source and the length of Fabry-Perot interferometer cavity. Metrological parameters of Fabry-Perot interferometer with different mirrors were compared. The presented thin diamond films may be an interesting alternative to the commonly used reflective surfaces.

Effect of growth temperature on the electrodeposition of zinc oxide layers on diamond surfaces

The electrochemical deposition of ZnO layers from an oxygenated zinc chloride bath has been realized on Boron Doped Diamond films as substrate for the first time. The influence of the bath temperature has been investigated from 20°C to 80°C. Scanning Electron Microscopy, X-Ray Diffraction and X-Ray Photoelectron Spectroscopy, performed on the treated surfaces, show the influence of the bath temperature on the composition, the structure and the morphology of the resulting deposits. For experiments made at 20°C, a thin and non-covering amorphous layer constituted of Zn(OH)2 is evidenced at the diamond surface. For deposits performed at bath temperatures equal or above 40°C, the diamond electrodes are covered with a few μm thick ZnO layer. However, X-Ray Photoelectron Spectroscopy analysis suggests the additional presence of Zn(OH)2 at the top surface of the zinc oxide deposits. The morphology and the crystallinity of these 2-D layers depend on the bath temperature. At 40°C, the film is constituted of big and smooth micrometric grains, while at 60°C the electrode is covered with closely packed and well crystallized ZnO micrometric rods. Finally, for the bath temperature of 80°C, the formation of nanorod-like and nanotube-like structures is observed. The main effects of increasing the bath temperature are the improvement of the crystallinity of the deposits, the texturation of the films along the direction perpendicular to the substrate surface and the increase of the deposited quantities.

The concentration gradient of boron along the growth direction in boron doped chemical vapor deposited diamond

The boron concentration in the growth direction of hot filament chemical vapor deposited boron doped diamond film is studied. Raman spectroscopy showed that the asymmetry of 1332cm−1 peak was enhanced in the growth direction. The estimated boron content from the position of the Lorentzian contribution to the 500cm−1 Raman feature and the electron probe microanalysis on the cross-section of the diamond film reveal a monotonically increasing of boron concentration in the film growth direction.

Understanding active chlorine species production using boron doped diamond films with lower and higher sp3/sp2 ratio

The present study was motivated by the reports that promote the use of boron doped diamond (BDD) anode for electrochemical disinfection. The discussion about the production of undesirable active chlorine species on diamond films is still open. For this reason, the influence of sp3/sp2 ratio on the performance on the evolution of chlorine-related species was investigated by polarization and electrolytic techniques in order to establish whether their formation and consumption related to either chemical or electrochemical reactions. The results demonstrated that dissolved Cl2, ClO2−, ClO2, ClO3− and ClO4− species can be electrochemically formed at both BDD electrodes. However, the concentration trends are different, indicating that the relation of sp3/sp2 ratio has a key role in the electrochemical route to produce ClO3− and ClO4−.

Electrochemical impedance spectroscopy of polycrystalline boron doped diamond layers with hydrogen and oxygen terminated surface

This work is a systematic study of electrochemical impedance spectroscopy of high quality polycrystalline boron doped diamond films with varying boron content (from semiconducting to metallic behavior) and with different surface terminations (hydrogen or oxygen) in aqueous electrolyte solution. The films were grown by microwave plasma enhanced chemical vapor deposition. The concentration of acceptors (NA) was determined from the Mott-Schottky plots and the values were compared with those from neutron depth profiling and Raman spectroscopy. The NA values are in a good agreement across the different techniques, ranging from ca. 1.2·1020cm−3 for semiconducting samples up to ca. 2·1021cm−3 for heavily doped films with metallic conductivity. The films with hydrogen terminated surface exhibit lower values of both the flat band potentials (Efb) and the NA values, compared to the films with oxygen terminated surface.

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

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

Selective secondary nucleation controlled (001)-texture in boron doped diamond films by increasing the concentrations of tetramethylsilane and trimethylborane

Diamond shows anisotropic physical and chemical properties, depending on its crystallographic orientations. Owing to the lack of large-scale single crystalline diamond substrates, however, the growth of textured diamond film becomes a popular way in tailoring its optical, electrical, mechanical, and thermal properties for specific applications. In the present study, we show that the (001)-texture of boron doped diamond (BDD) thin film can be controlled by a selective secondary nucleation process. To achieve this, a low concentration of tetramethylsilane (TMS) was introduced to induce a high secondary nucleation rate on the non-{001} diamond facets, hindering their lateral growth. In contrast, the continuous growth and expansion of the {001} facets are kept, which leads to the formation of (001)-textured diamond film. In addition, the orientation of the film can be continuously improved by increasing the concentration of either TMS or trimethylborane (TMB) in the gas phase within a relatively large parameter window. This study not only presents a new mechanism in controlling the textured of diamond, but also sheds some light on the fundamental research regarding the diamond growth.

Fabrication, characterisation and photocatalytic activity of TiO2 nanorods on boron doped diamond film through hydrothermal method

In order to achieve rapid and efficient decomposition of organic pollutants, semiconductor materials with heterostructure are applied because of the effective electron hole pair separation via the interfacial junction. Among the semiconductor materials, TiO2 and boron doped diamond (BDD) with unique excellent properties are ideal building blocks to form heterojunction structure, which can be used in waste water treatment. In this work, the TiO2 nanorods (NRs) with different morphology have been deposited on BDD films with a ZnO buffer layer via hydrothermal method. It is demonstrated that the reaction temperature has a great effect on the morphology and crystallinity of the TiO2 NRs on BDD film. The crystallinity of TiO2 NRs can be improved by increasing the reaction temperature. Experimentally, it shows that the TiO2 NRs/ZnO/BDD heterojunction shows enhanced photocatalytic activity with respect to TiO2 NRs/ZnO and TiO2 NRs/BDD heterojunctions respectively.

In situ reactivation of low-temperature thermionic electron emission from nitrogen doped diamond films by hydrogen exposure

Nitrogen doped, hydrogen terminated diamond films have shown a work function of less than 1.5eV and thermionic electron emission (TE) has been detected at temperatures less than 500°C. However, ambient exposure or extended operation leads to a deterioration of the emission properties. In this study thermionic electron emission has been evaluated for as-received surfaces and for surfaces after 18months of ambient exposure. The initial TE current density of the freshly deposited diamond film was ~5×10−5A/cm2 at 500°C. In contrast, the initial TE current density of a film aged for 18months was ~1.8×10−9A/cm2 at 500°C. The decreased emission current density is presumed to be a consequence of oxidation, surface adsorption of contaminants and hydrogen depletion from the surface layer. In situ reactivation of the aged film surface was achieved by introducing hydrogen at a pressure of 1.3×10−4mbar and using a hot filament of a nearby ionization gauge to generate atomic and/or excited molecular hydrogen. After 2h of exposure with the sample at 500°C, the surface exhibited a stable emission current density of ~2.3×10−6A/cm2 (an increase by a factor of ~1300). To elucidate the reactivation process thermionic electron energy distribution (TEED) and XPS core level spectra were measured during in situ hydrogen exposure at 5×10−8mbar. During the isothermal exposure it was determined that atomic or excited hydrogen resulted in a much greater increase of the TE in comparison to exposure to molecular hydrogen. During exposure at 400°C the surface oxygen was substantially reduced, the TEED cut-off energy, which indicates the effective work function, decreased by ~200meV, and the TE intensity increased by a factor of ~100. The increase in thermionic emission with hydrogen was ascribed to the reactivation of the surface through the formation of a uniform surface dipole layer and a reduction of the surface work function.