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

TL;DR

This paper demonstrates a method to fabricate and characterize three-dimensional graphitic microchannels inside single-crystal diamond using ion microbeam writing, revealing their structure, electrical properties, and potential applications.

Contribution

It introduces a precise technique for creating buried graphitic microchannels in diamond with controlled depth and demonstrates their electrical conductivity and stability after thermal treatment.

Findings

Microchannels extend within diamond in all three spatial directions.

Channels become conductive and stable as graphitic after high-temperature annealing.

Electrical characterization shows charge transport mechanisms depend on implantation fluence.

Abstract

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