Boron-doped Polycrystalline Diamond Films Research Articles

Heavily boron-doped polycrystalline diamond films: Microstructure, chemical composition investigation and plasma in-situ diagnostics

The introduction of boron brings excellent electrical conductivity to diamond films, but also induces uncontrollability of the doping process. Therefore, it is crucial to the monitor of the growth and doping processes. In this work, to establish the correlation between the gas-phase chemical reactions and the microstructure characteristics of heavily boron-doped diamond (BDD) films, the plasma reactions in the chemical vapor deposition (CVD) process of BDD films were in-situ diagnosed and monitored using optical emission spectroscopy (OES), and the effect of different B/C ratios (from 10,000 to 60,000 ppm) on the microstructure, chemical composition were investigated comprehensively. As the B/C ratio increases, the insufficient gas-phase excitation and the “hydrogen abstraction” reaction of BH species lead to a massive loss of H species in the gas-phase of plasma, which is unfavorable for the diamond growth, weakens the etching on sp2 carbon, induces the development of defects and seriously damages the diamond films quality. The in-situ diagnostics and monitoring of the plasma state can realize the optimization of the growth and doping process for heavily doped polycrystalline BDD films, which is highly significant for its preparation and application.

Image converter tubes with diamond photocathodes and electron flow multipliers

The results of investigations of solar-blind image converter tubes (ICTs), sensitive in the vacuum-ultraviolet (VUV) spectral range are presented. Sensitive-conversion layers of photocathodes based on boron-doped polycrystalline diamond films were grown up on sapphire substrates for the first time. Electron flow multipliers (EFMs) were fabricated in the form of diamond grid. Solar-blind VUV ICTs without the EFM are characterized by spectral sensitivity range of 180…250 nm, estimate of the threshold sensitivity value ~10-9 W/Hz0.5 and current sensitivity ~12 - 15 mA/W. Solar-blind VUV ICTs comprising the electron flow multipliers are characterized by extended spectral sensitivity range of 180…270 nm, improved estimate of the threshold sensitivity value 10-11… 5 × 10-12 W/Hz 0.5 and current sensitivity 50 mA/W.

Preparation and electrochemical properties of boron-doped polycrystalline diamond film with five-fold twin structure

In this study, boron-doped polycrystalline diamond (BDD) films were deposited on 6-inch silicon wafer by using microwave plasma chemical vapor deposition (MPCVD). Mixed gas containing hydrogen, methane, and diborane was used as precursor and the wafer temperatures were set at 750 °C, 850 °C and 950 °C, respectively. Five-fold twin structures were observed in the samples prepared at 850 °C and they promote the increase of surface roughness. Furthermore, these twin structures may lead to the increase of boron atoms at the surface, which was verified by first-principles calculation. BDD film that contains five-fold twin structures has higher Hall mobility, lower electrical resistivity and larger hole carrier concentrations at room temperature. Besides, reactive red X-3B (200 mg/L) was fully degraded by BDD electrodes at current density of 100 mA/cm2 within 40 min using NaCl as supporting electrolyte. Overall, BDD film electrodes prepared by appropriate methods contain a large quantity of five-fold twin structures surface have excellent electrochemical properties and thereby demonstrate potential as a promising waste water degradation material.

Sensitive Elements of High Temperature Pressure Sensors Formed from a Doped Polycrystalline Diamond

The need to create highly accurate pressure sensors that capable operate under extreme conditions in aviation, rocket and space equipment increases and becomes more relevant. The unique properties of diamond make it a promising material for microelectronic sensors. Sensitive elements of pressure sensors were developed where a resilient element is formed from silicon but resistance strain gauges are formed from a boron-doped polycrystalline diamond film.

Особенности характеристик солнечно-слепых электронно-оптических преобразователей с алмазными фотокатодами

The results of investigations of solar-blind image converter tubes (ICTs), sensitive in the ultraviolet spectral range are presented. Photocathodes sensitive layers of the ICT are based on boron-doped polycrystalline diamond films were grown up on sapphire substrates for the first time. Spectral range of the ICT sensitivity is 180…250 nm, the threshold sensitivity value without the electron flow multiplier ~ 10-9 W/Hz0.5 and spectral sensitivity ~ 12 - 15 mA/W.

Promising Superconducting Materials for Highly Sensitive Detectors of the Infrared and Terahertz Ranges

Modern technologies of photonics, astrophysics, medicine and security systems have a demand for development of new types of sensitive detectors and/or optimization of existing ones. As an example, a strong demand exists for improvement of the characteristics of highly sensitive detectors based on superconducting materials. One way to optimize the performance of such detectors is to select a suitable superconducting material. This is due to the fact that the technical characteristics of devices are determined by relaxation mechanisms of nonequilibrium processes that occur in the material upon absorption of electromagnetic radiation. In this paper, we focused on the study of the relaxation of nonequilibrium processes in superconducting materials such as highly boron-doped polycrystalline diamond films, highly disordered titanium nitride (TiN) films and ultrathin amorphous tungsten silicide films (WSi). The experimental data allowed us to determine the temperature dependence of the inelastic relaxation time in the studied materials. These results can help us to evaluate the applicability of these materials for the different types of superconducting detectors.

Electron affinity of undoped and boron-doped polycrystalline diamond films

The electron affinity of polycrystalline undoped and boron-doped diamond films was investigated by means of X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy. It was demonstrated that both as-grown and hydrogenated polycrystalline diamond films exhibited true negative electron affinity (NEA). Positive electron affinity (PEA) was observed after diamond surface oxidation in plasma. NEA reduction was observed after hydrogenation of the polycrystalline film surface in plasma. This effect was related to depolarization of the surface dipoles, an increase in the density of surface defects, and an increase in contaminations on the surface. Boron doping of the diamond film had a negligible effect on electron affinity. Downward surface band bending was found for all the samples that were studied, and there was larger band bending for polycrystalline diamond surfaces modified in plasma than for as-grown polycrystalline diamond surfaces.

Investigations on etching resistance of undoped and boron doped polycrystalline diamond films by oxygen plasma etching

The reactive ion etching (RIE) technique was used to etch the undoped and boron-doped diamond (BDD) polycrystalline films using oxygen plasma. The effect of boron within the BDD coatings on the morphology was investigated. BDD films exhibited much superior etching resistance than the undoped diamond films, wherein the (111) planes of BDD films were more etching resistant than (100) planes due to much higher boron concentration. However, this is in contradiction to undoped diamond films whose (111) planes were etched more quickly. The results would help to better design a particular and efficient etching method for undoped and BDD films to get a well-patterned microstructures.

Development of Conductive Boron-Doped Diamond Electrode: A microscopic, Spectroscopic, and Voltammetric Study.

Building on diamond characteristics such as hardness, chemical inertness and low electron emission threshold voltage, the current microscopic, spectroscopic and voltammetric investigations are directed towards improving the properties of electrode coating materials for their future use in clinical studies of deep brain stimulation via fast-scan cyclic voltammetry (FSCV). In this study we combine the capabilities of confocal Raman mapping in providing detailed and accurate analysis of local distributions of material constituents in a series of boron-doped polycrystalline diamond films grown by chemical vapor deposition, with information from the more conventional techniques of scanning electron microscopy (SEM) and infrared absorption spectroscopy. Although SEM images show a uniform distribution of film crystallites, they have the limitation of being unable to differentiate the distribution of boron in the diamond. Values of 1018–1021 atoms/cm3 of boron content have been estimated from the absorption coefficient of the 1290 cm−1 infrared absorption band and from the 500 cm−1 Raman vibration. The observed accumulation of boron atoms and carbon sp2 impurities at the grain boundaries suggests that very high doping levels do not necessarily contribute to improvement of the material’s conductivity, corroborating with voltammetric data. FSCV results also indicate an enhanced stability of analyte detection.

Conductivity of boron-doped polycrystalline diamond films: influence of specific boron defects

The resistivity of boron doped polycrystalline diamond films changes with boron content in a very complex way with many unclear factors. From the large number of parameters affecting boron doped polycrystalline diamond film’s conductivity we focused on the role of boron atoms inside diamond grains in terms of boron contribution to the continuum of diamond electronic states. Using a combination of theoretical and experimental techniques (plane-wave Density Functional Theory, Neutron Depth Profiling, resistivity and Hall effect measurements, Atomic Force Microscopy and Raman spectroscopy) we studied a wide range of B defect parameters — the boron concentration, location, structure, free hole concentration and mobility. The main goal and novelty of our work was to find the influence of B defects (structure, interactions, charge localisation and spins) in highly B-doped diamonds — close or above the metal-insulator transition – on the complex material charge transport mechanisms.

Preparation, characterization and electrochemical properties of boron-doped diamond films on Nb substrates

A series of boron-doped polycrystalline diamond films were prepared by hot filament (HF) chemical vapor deposition on Nb substrates. The effects of B/C ratio of reaction gas on film morphology, growth rate, chemical bonding states, phase composition and electrochemical properties of each deposited sample were studied by scanning electron microscopy, Raman spectra, X-ray diffraction, microhardness indentation, and electrochemical analysis. Results show that the average grain size of diamond and the growth rate decrease with increasing the B/C ratio. The diamond films exhibit excellent adhesion under Vickers microhardness testing (9.8 N load). The sample with 2% B/C ratio has a wider potential window and a lower background current as well as a faster redox reaction rate in H2SO4solution and KFe(CN)6 redox system compared with other doping level electrodes.

Electrochemical behaviour of (111) B-Doped Polycrystalline Diamond: Morphology/surface conductivity/activity assessed by EIS and CS-AFM

Electrochemical activity, morphology and surface electrical conductivity of Boron-Doped Polycrystalline Diamond films prepared by MPCVD have been investigated. Heterogeneous apparent rate constants of three different redox systems, [Fe(CN)6]3−/4−, [IrCl6]2−/3− and [Ru(NH3)6]3+/2+ have been measured by both Cyclic Voltammetry and Electrochemical Impedance Spectroscopy on<100>textured films with a predominance of (111) faces: first measurements have been done with [Fe(CN)6]3−/4− only on as grown samples, and secondly after a mild electrochemical pretreatment the three redox systems have been investigated. “As-grown” samples showed a moderate average activity which was related to the presence of a minority of electronically conducting areas among insulating zones. Electrochemical treatment in neutral conditions substantially increased the activity and heterogeneous apparent rate constants kapp for the three couples were measured in the range of 10−2cms−1 with a good stability in time. Current-sensing AFM images performed ex situ showed that the electrochemically pre-treated material presented a high superficial conductivity whereas the grown sample showed major area of low conductivity.

Correlation between Plasma OES and Properties of B-doped Diamond Films Grown by MW PE CVD

Boron doped polycrystalline diamond films were grown using MW PE CVD method. Optical emission spectra (OES) of MW-plasma in the region from 200 nm to 800 nm during boron doped polycrystalline diamond films growth were in situ investigated. Raman spectroscopy method was used for morphology investigation of grown polycrystalline diamond films. Also, absorption spectroscopy method was used for optical properties investigation of all grown films.

Influence of growth pressure on the electrical properties of boron-doped polycrystalline diamond films

Heavily boron-doped diamond films are synthesized by the hot-filament chemical vapor deposition method under the gas mixtures of H2, CH4 and trimethyl borate. The measurement results of scanning electron microscopy, Raman spectroscopy, X-ray diffractometer and electrical properties showed the morphologies, microstructures, carrier concentration and superconducting transition temperature for as-grown diamond films were dependent on the change of growth pressure, and specially its carrier concentrations could be adjusted from 1019 to 1021 cm−3 by increasing growth pressures from 2.5 to 5 kPa. And further, the effects of growth pressure on the film microstructural property and the doping level dependence of the superconducting transition temperature were discussed.

High-Performance Polycrystalline Diamond Micro- and Nanoresonators

Cantilever type MEMS resonators were fabricated using boron-doped (~5 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) and undoped polycrystalline diamond (poly-C) films that were grown at 600degC or 780degC. The resonator dimensions ranged from 500 mum long, 10 mum wide, and 0.7 mum thick to 40 mum long, 100 nm wide, and 0.6 mum thick. Resonance frequencies and quality factors Qs were measured in vacuum, 10 5 torr, over the temperature range of 23degC-400degC. The measured values of the temperature coefficient of the resonance frequency were in the range of -7.2- -25.6 ppm. degC <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and seemed to be related to changes in the Young's modulus with temperature. Undoped poly-C cantilevers exhibit Qs as high as 116 000, the highest value reported for a cantilever resonator fabricated from a polycrystalline film. A thermally activated relaxation process seems to limit the measured Q -values for the highly doped poly-C samples.

Evaluation of diamond gauge factor up to 500 °C

Gauge factors of boron-doped polycrystalline diamond films were investigated in the ranges from room temperature to 500 °C and from 0 to 0.07 MPa of applied pressure. A VCR fitting was used as a package for a measurement at high temperature. Undoped and boron-doped polycrystalline diamond films were deposited on a Si substrate by hot filament chemical vapor deposition (CVD) method. A chip was fabricated with bulk micro machining technique. The gauge factors were evaluated in the ranges from room temperature to 500 °C in furnace. The calculated values of the gauge factors were found to vary in a range of 5–241. The gauge factors decreased with increased temperature from room temperature to around 100–300 °C. However, with higher temperature up to 500 °C, it increased.

Boron-doped diamond — Grained Mott's metal revealing superconductivity

Reconsidering the experimental data on superconducting transition in heavily boron-doped polycrystalline diamond films, we have suggested an original theoretical model based on the concept of disordered Mott's metal in which the transport above T C is controlled by weak localization of holes. It has been shown that in the Kelvin temperature range the spins of holes occupying the neighboring weakly localized orbits must be strongly correlated and that just this effect, which is fully analogous to the Cooper pairing known in classical superconductors, can account for the existence of superconductivity transition in this material. The possible influence of grain boundaries on the superconducting transition is discussed in the framework of a simple model. Assuming thermal noise as a source voltage difference between adjacent grains, a phase diagram determining the region of stability of superconducting state depending on grain size is derived.

Specific features of 325 nm Raman excitation of heavily boron doped polycrystalline diamond films

A set of MPCVD films was prepared from 0.5% CH 4/H 2 and B 2H 6 with B/C in the gas phase from 0 to 8000 ppm. When the excitation wavelength of their Raman spectra is switched from 632.8 to 325 nm: The Fano induced dip switches from high to low wave number side of the “1332 cm − 1 ” signal. The deformation and the downward shift of this signal decrease. The G band, diamond second order, CH x bands appear. The evolution of these bands with increasing B / C is reported and discussed.

Non-destructive determination of the boron concentration of heavily doped metallic diamond thin films from Raman spectroscopy

Raman spectra of heavily boron doped polycrystalline diamond films prepared by MPCVD exhibit ‘500’ and ‘1220 cm −1’ structures on a wider boron range than the ‘Fano’ deformation of the ‘1332 cm −1’ peak of diamond induced by the metallic conductivity of these films. Therefore, these peaks were ascribed to the boron concentration rather than directly to the metallic conductivity of the films. The ‘500 cm −1’ wide peak down-shifts as the boron content in the film increases. It can be fitted satisfactorily by the sum of a Gaussian and a Lorentzian component. The wavenumber of the Lorentzian component exhibits a simple and accurate one-to-one relationship with the boron concentration. Therefore, analysis of the Raman spectra can be used as a non-destructive technique to deduce easily and without contact the boron concentration of diamond films in the range 2×10 20 to 10 22 cm −3.

Non-destructive determination of the boron concentration of heavily doped metallic diamond thin films from Raman spectroscopy

Raman spectra of heavily boron doped polycrystalline diamond films prepared by MPCVD exhibit ‘500’ and ‘1220 cm −1 ’ structures on a wider boron range than the ‘Fano’ deformation of the ‘1332 cm −1 ’ peak of diamond induced by the metallic conductivity of these films. Therefore, these peaks were ascribed to the boron concentration rather than directly to the metallic conductivity of the films. The ‘500 cm −1 ’ wide peak down-shifts as the boron content in the film increases. It can be fitted satisfactorily by the sum of a Gaussian and a Lorentzian component. The wavenumber of the Lorentzian component exhibits a simple and accurate one-to-one relationship with the boron concentration. Therefore, analysis of the Raman spectra can be used as a non-destructive technique to deduce easily and without contact the boron concentration of diamond films in the range 2×10 20 to 10 22 cm −3 .