Fabrication and electrical characterization of three-dimensional graphitic microchannels in single crystal diamond

Abstract

We report on the systematic characterization of conductive micro-channels\nfabricated in single-crystal diamond with direct ion microbeam writing. Focused\nhigh-energy (~MeV) helium ions are employed to selectively convert diamond with\nmicrometric spatial accuracy to a stable graphitic phase upon thermal\nannealing, due to the induced structural damage occurring at the end-of-range.\nA variable-thickness mask allows the accurate modulation of the depth at which\nthe microchannels are formed, from several {\\mu}m deep up to the very surface\nof the sample. By means of cross-sectional transmission electron microscopy\n(TEM) we demonstrate that the technique allows the direct writing of amorphous\n(and graphitic, upon suitable thermal annealing) microstructures extending\nwithin the insulating diamond matrix in the three spatial directions, and in\nparticular that buried channels embedded in a highly insulating matrix emerge\nand electrically connect to the sample surface at specific locations. Moreover,\nby means of electrical characterization both at room temperature and variable\ntemperature, we investigate the conductivity and the charge-transport\nmechanisms of microchannels obtained by implantation at different ion fluences\nand after subsequent thermal processes, demonstrating that upon\nhigh-temperature annealing, the channels implanted above a critical damage\ndensity convert to a stable graphitic phase. These structures have significant\nimpact for different applications, such as compact ionizing radiation\ndetectors, dosimeters, bio-sensors and more generally diamond-based devices\nwith buried three-dimensional all-carbon electrodes.\n