Room-temperature fabrication of Schottky diodes was demonstrated for p-type boron-doped diamond. This fabrication method’s key technique is selective modification of surface termination from monohydride into oxygen groups using vacuum ultraviolet light irradiation in oxygen. The Au contacts, formed on the hydrogen-terminated surface, maintained Ohmic properties after this selective surface oxidation. The Au contacts then deposited on the oxidized surface, imparting Schottky properties. The lateral-type diodes comprising Au Schottky contacts and Au Ohmic contacts showed blocking voltage higher than 1 kV without electrode guarding. The leakage current at 1 kV was as low as 30 pA.
Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are complementary techniques providing respectively chemical and structural information on the sample target. These techniques are increasingly used together in Earth and Planetary sciences, and often together. LIBS is locally destructive for the target, and the laser-induced effects due to LIBS laser shots on the structure and on the Raman fingerprint of a set of geological samples relevant to Mars are here investigated by Raman spectroscopy and electron microscopy. Experiments show that the structure of samples with low optical absorption coefficients is preserved as well as the structural information carried by Raman spectra. By contrast, minerals with high optical absorption coefficient can be severely affected by LIBS laser shots with local amorphization, melting and/or phase transformation. Thermal modelling shows that the temperature can reach several thousands of degrees at the surface for such samples during a LIBS laser shot, but decreases rapidly with time and in space. In 2020, NASA Mars 2020 mission will send a rover equiped with a combined LIBS/Raman instrument for remote analysis (SuperCam) as well as fine-scale instruments for X-ray fluorescence (Planetary Instrument for X-Ray Lithochemistry-PIXL) and deep UV Raman spectroscopy (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals-SHERLOC) for proximity science. We discuss the implications of our results for the operation of these instruments and show that (i) the SuperCam analytical footprint for Raman spectroscopy is many times larger than the LIBS crater, minimizing any effects and (ii) SHERLOC and PIXL analysis may be affected if they analyze within a LIBS crater created by SuperCam LIBS.
We investigated the performance of Schottky diodes fabricated on diamond surface oxidized by two different techniques. A detailed comparison shows vacuum ultraviolet (VUV) light technique has better performance than the standard wet chemical technique: ideality factor and Schottky barrier height are more reproducible and leakage current is lower, suggesting VUV light oxidation method improves the controllability and the homogeneity of the surface electronic properties.
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