The flame spray pyrolysis of alcohol-soluble precursors allows the synthesis of mullite-composition nanopowders (average size of ϳ60 -100 nm) that, when annealed carefully, provide processable nano-mullite powders. The powders have been characterized using several spectroscopic and microscopy methods, including thermal gravimetric analysis, differential thermal analysis, diffuse reflectance infrared Fourier transform spectroscopy, and transmission electron microscopy. Preliminary studies on the pressureless-sintering behavior of these powders are presented. Without additives or any efforts to optimize the process, powder compacts could be sintered to relative densities of >90%, with grain sizes of <500 nm at 1600°C.

International audienceDefects induced by boron doping in diamond layers were studied by transmission electron microscopy. The existence of a critical boron doping level above which defects are generated is reported. This level is found to be dependent on the CH 4 /H 2 molar ratios and on growth directions. The critical boron concentration lied in the 6.5–17.0 10 20 at/cm 3 range in the <111> direction and at 3.2 10 21 at/cm 3 for the <001> one. Strain related effects induced by the doping are shown not to be responsible. From the location of dislocations and their Burger vectors, a model is proposed, together with their generation mechanism

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AIN/diamond heterostructures are very promising for high frequency surface acoustic wave (SAW) resonators. In their design, the thickness of the piezoelectric film is one of the key parameters. On the other hand, the film material quality and, hence, the device performance, also depend on that thickness. In this work, polished microcrystalline diamond substrates have been used to deposit AIN films by reactive sputtering, from 150 nm up to 3 um thick. A high degree of the c-axis orientation has been obtained in all cases. SAW one port resonators at high frequency have been fabricated on these films with a proper combination of the film thickness and transducer size.

Concerning diamond-based electronic devices, the H-terminated diamond surface is one of the most used terminations as it can be obtained directly by using H2 plasma, which also is a key step for diamond growth by chemical vapour deposition (CVD). The resultant surfaces present a p-type surface conductive layer with interest in power electronic applications. However, the mechanism for this behavior is still under discussion. Upward band bending due to surface transfer doping is the most accepted model, but has not been experimentally probed as of yet. Recently, a downward band bending very near the surface due to shallow acceptors has been proposed to coexist with surface transfer doping, explaining most of the observed phenomena. In this work, a new approach to the measurement of band bending by angle-resolved X-ray photoelectron spectroscopy (ARXPS) is proposed. Based on this new interpretation, a downward band bending of 0.67 eV extended over 0.5 nm was evidenced on a (100) H-terminated diamond surface.