  We report on the structural modifications induced by a lambda = 532 nm
ns-pulsed high-power laser on sub-superficial graphitic layers in
single-crystal diamond realized by means of MeV ion implantation. A systematic
characterization of the structures obtained under different laser irradiation
conditions (power density, number of pulses) and subsequent thermal annealing
was performed by different electron microscopy techniques. The main feature
observed after laser irradiation is the thickening of the pre-existing
graphitic layer. Cross sectional SEM imaging was performed to directly measure
the thickness of the modified layers, and subsequent selective etching of the
buried layers was employed to both assess their graphitic nature and enhance
the SEM imaging contrast. In particular, it was found that for optimal
irradiation parameters the laser processing induces a six-fold increase the
thickness of sub superficial graphitic layers without inducing mechanical
failures in the surrounding crystal. TEM microscopy and EELS spectroscopy
allowed a detailed analysis of the internal structure of the laser irradiated
layers, highlighting the presence of different nano graphitic and amorphous
layers. The obtained results demonstrate the effectiveness and versatility of
high-power laser irradiation for an accurate tuning of the geometrical and
structural features of graphitic structures embedded in single crystal diamond,
and open new opportunities in diamond fabrication.
