M. Bernard

Boron doped diamond electrodes for nitrate elimination in concentrated wastewater

Electrochem. and phys. properties of polycryst. B-doped diamond electrodes with a metallic conduction grown by MPCVD and HFCVD were studied with the goal to use them as cathodes, for the electrochem. redn. of nitrate in neutral solns. All electrodes contain a mean B concn. [B] >3 * 1020/cm3 and show a significant redn. of nitrate. However, the higher efficiency is obtained for the electrode having the highest [B] (1.5 * 1021/cm3) and the lowest concn. of parasitic phases. The anal. of the Raman spectrum proved to be a valuable tool to probe these characteristics. Quant. anal. of the solns. showed that the relative concns. of the nitrogenous species formed during the redn. of nitrates at -2 V do not depend on the B doping level. [on SciFinder (R)]

Pure paramagnetic behavior in Mn-doped ZnO semiconductors

Polycrystaline Mn-doped zinc oxides (Zn1−xMnxO) were synthesized by coprecipitation method with x varying between 0.01 and 0.1. Raman spectroscopy indicates the appearance of an additional mode which is an indicator for the incorporation of Mn ions into the ZnO host matrix. The magnetic properties have been studied by electron paramagnetic resonance (EPR) spectroscopy. The Mn-related EPR spectra exhibit the expected pattern for isolated Mn ions. Temperature dependence of the reciprocal integrated EPR signal follows a Curie law indicating a typical paramagnetic behavior for x⩽0.05.

Hydrogen-acceptor interactions in diamond

Abstract Hydrogen-acceptor interactions are investigated in boron-doped diamond through deuterium diffusion experiments followed by SIMS measurements and through infrared absorption spectroscopy. From deuterium diffusion, we show that BD interactions can be properly demonstrated in low compensation B-doped homoepitaxial layers. However, the presence of defects in such layers strongly affects this interaction. The degree of passivation of boron acceptors by deuterium depends on the diffusion temperature. At 550°C or below, the B and D concentrations exactly match giving rise to a complete disappearance of the absorption bands related to the electronic transitions of neutral boron acceptors. Under thermal annealing above 500°C, (B,D) pairs dissociate and neutral boron acceptors recover. At deuterium diffusion temperatures of 700°C, the B passivation is absent.

Hydrogen diffusion in B-ion-implanted and B-doped homo-epitaxial diamond: passivation of defects vs. passivation of B acceptors

Drastic differences in diffusion of H (deuterium) in diamond, B-doped by ion implantation and during homo-epitaxial film growth, and its influence on electrical properties are found by SIMS depth profiling, and by electrical (Hall effect) measurements. Type IIa natural diamond, B-doped by ion implantation and high quality homo-epitaxial B-doped diamond films were subjected to D plasma treatment under similar conditions. The results of SIMS measurements clearly show a huge difference in D diffusion profile for these two samples. While the sample doped during growth was totally deuterated, the implanted one showed only minor D penetration. Electrical measurements indicated that while the homo-epitaxial samples became insulating or showed strong decrease in their free hole concentration following deuteration, the identical treatment to the B-ion implanted sample caused only slight changes in electrical properties. The electrical properties and their dependence on annealing are correlated with the deuterium diffusion into diamond. A possible mechanism of (B, H) and (defect, H) pair formation is suggested as a possible explanation of the observed differences.

Hydrogen in n-type diamond

c ´´ Abstract The incorporation of hydrogen in n-type diamond has been investigated through its non-intentional introduction during the growth and through post-growth diffusion experiments. In the first case, (111) n-type diamond homoepitaxial films doped with phosphorus have been grown by microwave plasma chemical vapor deposition from a CH qD mixture. The phosphorus 42 concentrations were in the range 1.3=10 -3=10 cm . The concentration of deuterium incorporated is usually 100 times 18 19 y3

Optical Conductivity Studies in Heavily Boron‐Doped Diamond

The optical transmittance and reflectance of heavily boron-doped (2 × 10 20 cm -3 < [B] < 2 × 10 21 cm -3 ) epitaxial diamond layers deposited by MPCVD were measured in the infrared range. While T-dependent measurements confirmed the metallic character of such films, the overall spectral features were well reproduced by introducing Drude components in the fitting expression for the optical conductivity. The associated microscopic transport parameters were quantitatively compared to those resulting from preliminary transport measurements performed on the same samples. We show that room-temperature FTIR reflectance measurements provide an easy contactless characterization of the transport properties of such p + films, and we discuss what new information on carrier-phonon interaction as well as on the transport mechanism in the impurity band might be gained from temperature-dependent spectroscopic data.

Etching of p- and n-type doped monocrystalline diamond using an ECR oxygen plasma source

Abstract Simultaneous etching of NID, lightly boron-doped, phosphorus-doped homoepitaxial CVD films and Ib HPHT crystal was achieved at RT in a home-made reactor producing O2 ECR plasma which was homogeneous on approximately 200 cm−2. Etching rates varying from 60 (at −30 V) to 40 or 120 nm/min (at −140 V) are obtained with n- or p-type-doped samples, respectively. These etching rates are higher than those with O2 RF plasma, and those with previous inhomogeneous O2 ECR plasma with samples at 100 °C.

Detection of CHx bonds from micro Raman spectroscopy on polycrystalline boron doped diamond electrodes

MicroRaman signals excited at 457.8 nm have been obtained from some areas of heavily boron doped polycrystalline diamond films which have been used for electrochemical reactions. We could identify sp3 CH, CH2, CH3, all with narrow full width at half maximum. From comparisons to IR absorption from the bulk of undoped films and from the (111) and (100) surfaces of IIa crystal, and to Raman signals from the bulk of undoped polycrystalline films, we ascribed our micro Raman signals to CHx from the film surface. The sp3 CH2 and CH3 components appear more stable than the sp3 CH under CW laser exposure. This implies chemical bonding of H with C atoms of the film surface for all the sp3 CHx sites. This difference with the CHx at the surface of IIa crystals might originate from the heavy boron-doping of our films.

Conductivity and photoconductivity in boron doped diamond films: Microwave measurements

We used the microwave technique to measure electrical properties of heavily boron doped diamond films. This technique overcomes problems such as the presence of parasitic resistance due to the electrical contacts. The conductivity of these films is rather high (about 104 S m−1). The measured microwave conductivity has the same values as the dc conductivity. The conductivity varies with the doping. The highest value of conductivity does not appear for the highest value of doping, because of the presence of a parasitic phase. This will be proved by electron spin resonance and Raman spectra. Theoretical calculation rules out the skin effect in our measurements. It will be also possible to perform microwave photoconductivity measurements. The photoconductivity behavior varies in the opposite way to the conductivity. One explanation, based on the recombination time which decreases with the conductivity, will be presented.