Doped Diamond Films Research Articles

Enhanced deuterium diffusion in boron doped monocrystalline diamond films using bias-assisted MPCVD

The present study well emphasises the role of the bias voltage on the deuterium diffusion in boron doped diamond films ( [ B ] = 2 × 10 19 cm − 3 ) . A − 50 V bias voltage applied between the deuterium microwave plasma and the diamond surface is required to initiate deuterium diffusion. Increasing effective diffusion coefficients are obtained from the SIMS profiles for bias voltages up to − 80 V . Then, for bias voltages higher than − 120 V , the etching of diamond film becomes dominant.

Dose rate effects on the performance of MWCVD diamond films as TL gamma radiation dosimeter

AbstractDose rate effects on the thermoluminescence (TL) properties of undoped and 750 ppm nitrogen doped microwave chemical vapor deposition (MWCVD) diamond films were analyzed. The diamond samples were exposed to 2.4–20.67 Gy/min dose rates from a 60Co source. The TL glow curve of undoped sample showed no apparent dose rate effects. The doped diamond film exhibited dose rate effects consisting in a 10–30% integrated TL increase as the dose rate increased. The TL response as a function of dose rates showed a nonlinear behavior for the doped sample contrary to the undoped diamond film. The dose rate effects were evaluated through the determination of the kinetics parameters by fitting of the TL glow curves. The results indicate that chemical vapor deposition (CVD) diamond may present some dose rate effects on the TL properties in a given dose range, implying that some care should be exercised in order to use CVD diamond films in radiation dose assessments.

Free-standing boron doped CVD diamond films grown on partially stabilized zirconia substrates

Boron doped diamond films have been grown adhered to silicon substrates by chemical vapor deposition using boron containing gases. In this work it was shown that it is possible to grow free-standing boron doped CVD diamond films on partially stabilized zirconia substrates using boron powder as the source for doping. Results from Raman spectroscopy confirmed the boron incorporation with concentration up to ∼10 20 cm −3. X-ray diffraction and scanning electron microscopy showed that the effect of boron incorporation in the microstructure of the diamond film is negligible. The measurement of the resistivity as a function of temperature confirmed the semiconductor behavior, as expected for p-type diamond.

Carbon monoxide sensing at room temperature via electron donation in boron doped diamond films

Abstract We report room temperature detection of carbon monoxide (CO) below 100 parts per million in air using boron doped diamond films prepared by hot filament chemical vapor deposition method. Gas sensing characteristics are observed to be improved with larger grain size in the films. Sensing characteristics for 100 ppm CO with response time of 30 s and recovery times of ∼50 s at room temperature show the excellence of boron doped diamond as CO sensor material. The lowest values of response time ∼5 s and recovery time ∼20 s were observed for BDD with grain size of 1 μm for 1000 ppm of CO in air. The carbon monoxide sensing mechanism is attributed to electron donation to p-type boron doped diamond as a result of CO oxidation on its surface.

Hybrid superconducting nanostructures: very low temperature local probing and noise

We review the topic of hybrid superconducting nanostructures by introducing the basic physical concepts and describing recent key experimental results. We discuss the superconductivity nucleation in mesoscopic structures, the vortex lattice imaging in doped diamond films, the superconducting proximity effect, multiple Andreev reflection in Josephson junctions and the electronic micro-cooling in hybrid tunnel junctions. An emphasis is put on very low temperature local probes and noise measurement techniques developed in Grenoble.

The influence of boron content on electroanalytical detection of nitrate using BDD electrodes

Electrochemical response of nitrate reduction was analyzed using Boron Doped Diamond (BDD) films grown with different boron levels and it was correlated with the electrode physico-chemical properties. X-ray photoelectron spectroscopy and contact angle measurements showed the evolution of oxygen content and the weattability associated to the chemical surface modification as boron content increase in such films. Raman spectroscopy showed that the broad peaks at 1220 and 500 cm −1 become more evident with the boron addition. Electrochemical measurements by square wave voltammetry for nitrate reduction showed a strong dependence between the doping level of the BDD film and the nitrate detection. BDD film grown with B/C ratio of 20,000 ppm presented the best sensibility to low concentration of nitrate. This result was analyzed from the linear relationship between the peak currents as a function of the nitrate concentration. This behavior was attributed to the changes in the diamond surface chemical and the film grain size.

Boron Doped Diamond Films Surface Modification with Copper and Palladium Nanoparticles Obtained by Electrodeposition

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Thermionic electron emission from low work-function phosphorus doped diamond films

Thermionic electron emitters are a key component in applications ranging from travelling wave tubes for communications, space propulsion and direct energy conversion. As the conventional approach based on metallic emitters requires high operating temperatures the negative electron affinity (NEA) characteristic of diamond surfaces in conjunction with suitable donors would allow an electronic structure corresponding to a low effective work function. We have thus prepared phosphorus-doped polycrystalline diamond films on metallic substrates by plasma assisted chemical vapor deposition where an NEA surface characteristics was induced by exposure of the film surface to a hydrogen plasma. Thermionic electron emission measurements in an UHV environment were conducted with respect to the Richardson–Dushman relation observing an emission current at temperatures < 375 °C. Measurements were terminated at 765 °C without significant reduction in the electron emission current indicating a stable hydrogen passivation of the diamond surface. A fit of the emission data to the Richardson equation allowed for the extraction of emission parameters where the value of the materials work function was evaluated to 0.9 eV. This value could well be the lowest measured work function of any known material.

Characterization of homoepitaxial and heteroepitaxial diamond films grown by chemical vapor deposition

Sulphur-doped and boron-sulphur co-doped diamond thin films were prepared by using chemical vapour deposition on p-type Si (100) and HTHP-diamond (100) substrates. The structures and properties of CVD diamond films were investigated with atom force microscope (AFM), Raman spectrum, sanning tunneling microscopy (STM) and current imaging tunneling current spectroscopy (CITS). Comparing the structures and properties of the doped diamond films grown on Si and HTHP diamond substrates, we find that the films deposited on Si substrates are composed of spherical grains with size of one hundred nanometer, the doped diamond films on Si substrates consist of large grains with a high fraction of grain boundaries due to the successive secondary nucleation,and the roughness of the films is estimated to be around 18.5nm. The doped diamond films on HTHP diamond substrates are composed of nanometer crystal grains with the sizes of 10—50nm and the film surface is flat with the roughness estimated to be around 1.8nm. Raman and resistivity measurements reveal that the films deposited on HTHP diamond substrates have much higher quality, fewer defects and lower stress, and higher conductivity than the films grown on Si substrates. Current imaging tunnelling current spectroscopy (CITS) images indicate that some grain boundaries and crystalline facets near the grain boundaries are he high electron emission regions. However, the grain boundaries and crystalline facets of the doped diamond films on HTHP diamond substrates have uniform electron emission currents, which indicates that the doped atoms are uniformly distributed in that films. The local I-V characteristics for films deposited on Si or HTHP diamond substrates indicate the n-type conduction.

Low temperature onset for thermionic emitters based on nitrogen incorporated UNCD films

Thermionic electron emission is a key phenomenon utilized in a variety of applications, from communications, space propulsion to direct energy conversion. Doped diamond films with a negative electron affinity (NEA) surface characteristic present a reduced effective work function for electron emission. Our prior research has indicated a work function of ∼ 1.5 eV for nitrogen doped diamond films prepared by microwave plasma CVD. The focus of this study is on the role of the interfacial or nucleation layer. A thermionic emitter was fabricated with a nitrogen incorporated ultra-nanocrystalline diamond (UNCD) nucleation layer and a nitrogen doped diamond surface layer with hydrogen termination. The film exhibited a resistance that decreased with temperature suggesting the role of the dopant, and thermionic electron emission was observed at temperatures < 250 °C. An analysis based on the Richardson–Dushman equation indicated an emission barrier of < 1.3 eV with a Richardson constant of ∼ 0.8 A/cm 2 K 2.

Optical emission study of a doped diamond deposition process by plasma enhanced chemical vapor deposition

Standard H2∕CH4∕B2H6 plasmas (99% of H2 and 1% of CH4, with 0–100ppm of B2H6 added) used for doped diamond film growth are studied by optical emission spectroscopy in order to gain a better understanding of the influence of boron species on the gas phase chemistry. Only two boron species are detected under our experimental conditions (9∕15∕23Wcm−3 average microwave power density values), and the emission spectra used for studies reported here are B(S1∕22−P1∕2,3∕202) and BH[AΠ1-XΣ+1(0,0)]. Variations of their respective emission intensities as a function of the ratio B∕C, the boron to carbon ratio in the gas mixture, are reported. We confirmed that the plasma parameters (Tg, Te, and ne) are not affected by the introduction of diborane, and the number densities of B atoms and BH radical species were estimated from experimental measurements. The results are compared to those obtained from a zero-dimensional chemical kinetic model where two groups of reactions are considered: (1) BHx+H↔BHx−1+H2 (x=1–3) by analogy with the well-known equilibrium CHx+H set of reactions, which occurs, in particular, in diamond deposition reactors; and (2) from conventional organic chemistry, the set of reactions involving boron species: BHx+C2H2 (x=0–1). The results clearly show that the model based on hydrogen and boron hydrides reactions alone is not consistent with the experimental results, while it is so when taking into account both sets of reactions. Once an upper limit for the boron species number densities has been estimated, axial profiles are calculated on the basis of the plasma model results obtained previously in Laboratoire d’Ingénierie des Matériaux et des Hautes Pressions, and significant differences in trends for different boron species are found. At the plasma-to-substrate boundary, [BH] and [B] drop off in contrast to [BH2], which shows little decrease, and [BH3], which shows little increase, in this region.

Nontraditional Electrode Materials in Environmental Analysis of Biologically Active Organic Compounds

AbstractThis review describes recent results regarding voltammetric and amperometric determination of submicromolar concentrations of various environmentally important biologically active organic substances using nontraditional types of electrodes either in batch analysis or in flow liquid systems (especially HPLC or FIA with electrochemical detection). Attention is paid to solid amalgam electrodes (environmentally friendly alternatives to mercury electrodes), to carbon paste electrodes with easily renewable surface, to boron doped diamond film electrodes with very low noise and broad potential window, and to inexpensive solid composite electrodes with high signal‐to‐noise ratio, compatibility with organic solvents and easy mechanical or electrochemical pretreatment. The review concentrates on our own results in the context of the general development in the filed.

A positron annihilation study on the defect properties of doped diamond films

Doppler broadening measurements were performed on undoped, boron doped, and sulfur doped diamond films. The defect properties in these different diamond films were analyzed and the effect of boron concentration in the B-doped diamond films on these properties was studied. The Doppler broadening measurements were characterized with the shape parameter S and the wing parameter W. From these fitted characteristic S and W values of the diamond films and plots of S vs. position implantation energy, it was deduced that undoped and S-doped diamond films are rich of vacancy-like defects, while B-doped diamond films are poor of vacancy-like defects. This difference may originate from possible different charge state of the vacancy-like defects and from the incorporation of impurities in the different growth ambient of the films. By comparing the parameters obtained in the Doppler broadening measurements of diamond films with different boron concentration, we found that S values of B-doped diamond did not decreased with the increasing of boron concentration, which suggests that more damaged regions form in the higher boron concentration samples.

Highly and heavily boron doped diamond films

From the high ionization energy E i = 0.368 eV and high solid solubility ≥ 1.4 × 10 22 cm − 3 of boron in diamond, metallic conductivity is expected on the boron impurity band within the band gap (Mott model). On the contrary, the numerical models used to describe the superconductivity of metallic diamond mainly use the Bardeen model with a Fermi level within the valence band. Taking into account the decrease to zero of E i through the high [B] range and the band gap narrowing through the high and heavy [B] ranges, both specific of the Bardeen model, we discuss the validity of the Mott and Bardeen models from the literature and cathodoluminescence and Raman experiments. They agree with the Mott rather than the Bardeen model. Several experiments independently show the coupling of boron related levels with the zone centre optical phonons which soften for heavy [B]. The Mott model might explain the similar range of the superconductivity temperature of homoepitaxial and polycrystalline films from the similarity of their boron impurity band.

Field penetration and its contribution to field enhanced thermionic electron emission from nanocrystalline diamond films

Field emission from sulfur doped nanocrystalline diamond films is characterized by intense emission sites with nm scale diameters. Field emission measurements were obtained at room temperature and analyzed in terms of the Fowler–Nordheim expression where electron emission is due to tunneling through a diminished barrier. The electron emission versus temperature was also recorded at a series of applied fields from 0.5 to 0.8 V/μm. These results were analyzed in terms of a modified Richardson–Dushman relation which describes field dependent thermionic emission. It was found that both sets of data could be fit with a work function of 2.0 eV and a field enhancement factor of ∼ 1750. The large field enhancement could not be correlated with specific structures on the relatively flat surfaces. The field and thermionic-field emission from the sulfur doped nanocrystalline diamond films is evaluated by a model which includes barrier lowering as a result of field penetration effects.

An investigation of structural and electrical properties of boron doped and undoped nanocrystalline diamond films

AbstractNanocrystalline and microcrystalline undoped and boron doped diamond films are investigated by means of SEM, Raman and photocurrent techniques. SEM measurements on nanocrystalline diamond show the typical diamond columnar structure whereas for microcrystalline diamond such structure is not observed. Raman investigation shows a clear diamond peak at 1332 cm–1 for all investigated films and a Fano resonance is observed for the microcrystalline sample prepared with 2000 ppm of boron in the gas mixture indicating a transition into the semi‐metallic state. Photocurrent measurements also show a presence of boron in some films. It is found that when temperature is decreased lower than 80 K, the boron photocurrent threshold in the case of NCD material behaves differently compared to bulk diamond. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Surface Characterization of Sequential Electrodeposited Methanol Electrocatalysts on HOPG, Vulcan and Boron Doped Diamond Films

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Detection of N and B in doped diamond films by ERDA method and related electrochemical characteristics

Boron and nitrogen incorporation in diamond films grown by hot filament chemical vapor deposition (HFCVD) was investigated by elastic recoil detection analysis (ERDA). Boron concentration of only B-doped films ranges from 0.3% to 1.7%, which is related to the increase of B concentration into the gas phase from 0.2% to 1.5%. Two different sets of diamond films co-doped with B and N were investigated. The B incorporation into the films varied from 0.17% to 0.29% while the B concentration in the gas phase is increased from 0.2% to 2.0% and the N concentration in the films remains fixed. If the N 2 concentration of gas phase increases from 0.7% to 4.8% at a fixed B concentration, the B/C ratio of the films remains virtually unchanged (0.1 to 0.17%). Our results obtained from Scanning Electron Microscope (SEM), Raman Spectroscopy and 4 points resistivity measurements demonstrated that nitrogen incorporation modifies the characteristics of B-doped diamond films. In this article we also discuss the effect of film doping on the diamond electrode working potential window, which has been extended from 3.0 V to 3.5–4.0 V.

Superconductive B-doped nanocrystalline diamond thin films: Electrical transport and Raman spectra

Electrical transport properties of thin boron doped nanocrystalline diamond films with thicknesses of 60–500nm have been studied. The Raman spectra measured exhibit Fano resonances, characteristic for B concentrations close to the metal-to-insulator transition. Upon increasing the B concentration, the sp2 carbon related Raman resonances vanish. In such boron-doped nanocrystalline diamond films, a positive magnetoresistance could be observed at liquid helium temperatures. The boron doped diamond films show conductivity similar to that of B-doped epitaxial diamond without any significant contribution of the grain boundary transport, leading to the superconductive transition in nanocrystalline diamond at ∼1.66K.

Neutron transmutation of 10B doped diamond

Free standing 10B isotope doped diamond films deposited by chemical vapor deposition in a microwave chamber were irradiated to thermal neutron fluence values of 0.32 × 10 19, 0.65 × 10 19, 1.3 × 10 19, and 2.6 × 10 19 n/cm 2. Cooling of the diamond films was maintained during irradiation. In a separate experiment, neutron irradiation to a total fluence of 2.4 × 10 20 n/cm 2 with equal fast and thermal neutrons was also performed on a diamond epilayer without cooling during irradiation. The formation of defects in the diamond films was characterized using Raman, FTIR, photoluminescence, electron paramagnetic resonance spectroscopy, and X-ray diffraction. It was found that defect configurations in diamond responsible for an increase in continuum background in the one-phonon region of Raman spectrum were absent in the films that have been cooled. The FTIR peak at 1530 cm − 1 annealed in the sample irradiated to a fluence of 2.6 × 10 19 n/cm 2 indicating that the sample reached a temperature of 300 °C during irradiation. Absence of characteristic infrared absorption peaks that were observed only upon annealing neutron irradiated diamond is used to conclude that the temperature of the sample during neutron irradiation to a fluence of 2.6 × 10 19 n/cm 2 was well below 650 °C needed for mobility of defects and accumulation of stable unrecoverable damage. On the other hand, results from diamond epilayer subjected to equal thermal and fast neutron fluence of 2.4 × 10 20 n/cm 2 and without cooling showed that defects formed from displaced carbon atoms became mobile and formed complex configurations of irrecoverable damage. Electrical conductance of the unirradiated and irradiated diamond samples was measured as a function of temperature to determine the compensation of the p-type by the n-type charge carriers.