  In the present work we report about a parallel-processing ion beam
fabrication technique whereby high-density sub-superficial graphitic
microstructures can be created in diamond. Ion beam implantation is an
effective tool for the structural modification of diamond: in particular
ion-damaged diamond can be converted into graphite, therefore obtaining an
electrically conductive phase embedded in an optically transparent and highly
insulating matrix. The proposed fabrication process consists in the combination
of Deep Ion Beam Lithography (DIBL) and Focused Ion Beam (FIB) milling. FIB
micromachining is employed to define micro-apertures in the contact masks
consisting of thin (<10 um) deposited metal layers through which ions are
implanted in the sample. A prototypical single-cell biosensor was realized with
the above described technique. The biosensor has 16 independent electrodes
converging inside a circular area of 20 um diameter (typical neuroendocrine
cells size) for the simultaneous recording of amperometric signals.
