Cleavage-Driven Laser Writing in Monocrystalline Diamond

The propagation of graphitization wave through the diamond bulk under multipulse laser irradiation is a largely self-guided process. This fact assists the production of graphitized wires oriented along a laser beam and greatly complicates formation of the structures oriented differently. Here, we develop new approaches to control laser graphitization that should empower the potential of 3D laser microstructuring inside a diamond crystal. Two techniques are investigated: (i) a laser seed damage of crystal with subsequent exposure at a lower laser fluence, thus restricting the propagation of the graphitization wave toward the beam and (ii) formation of a dominant microfracture perpendicular to the laser beam, thus guiding growth of the graphitized thread

Very long laser-induced graphitic pillars buried in Single-Crystal CVD-Diamond for 3D detectors realization

The morphology, optical, spectroscopic and electrical characterization of mm-long graphite pillars created by picosecond pulsed laser irradiation ( λ = 800 nm and 1 kHz of repetition rate), buried in single crystal CVD diamond to be employed as electrodes in a 3D diamond detector, is reported. The array of graphitized columns – 2.5 mm-long, with a diameter of ≈ 10 µ m – consisted of two rows spaced by 110 µ m with 12 pillars in each, which formed an interdigitated electrode structure embedded in the diamond crystal bulk. The presence of stressed regions along and between pillars were clearly shown with optical polarized microscopy, in a black field configuration. Confocal micro-Raman and photoluminescence analysis has been employed to scan local stresses, both generated around the graphitic wires and also developed on the pillars’ plane. Defected / stressed regions with diameter of the order of 10 µ m surrounding the individual pillars was measured, and paired carbon interstitials (3H defects) were also revealed. For the investigated structure, detrimental e ff ects induced by such structural defects, clearly produced by laser-induced diamond-graphite transition, as well as the presence of a relatively high voltage drop along the graphitized pillars related to their own geometry have been reflected on the charge carriers collection performances evaluated under MeV β-particles. The creation of electronic active states within the diamond bandgap, as emphasized by spectral photoconductivity characterization, would play a fundamental role in lowering lifetime of generated carriers and then the detector collection e ffi ciency. Indeed, states located in the middle of the diamond bandgap, acting as e ffi cient recombination centers and decreasing the lifetime of generated carriers, drastically reduce the mean drift path of barriers and then the overall detector collection e ffi ciency, as evaluated in the examined structure even at the highest applied voltages (up to 600 V)

Buried graphite electrodes in single crystal CVD Diamond investigated with MeV protons and electrons

The paper reports the study of an asymmetric detector with graphite contacts, about 20 µ m in diameter, buried within a synthetic single crystal diamond. To induce diamond-to-graphite transformation a femtosecond IR laser is used on the surface and bulk volume. Optical microscopy with crossed polarizers has evidenced optical anisotropy laterally the buried pillared contacts whereas the regions between pillars exhibited the presence of both tensile and compressive stress there around, as revealed with Raman spectroscopy mapping. Notwithstanding the strain, the buried electrodes showed linear electrical response and demonstrated ability to collect the charge carriers produced by 3.0 and 4.5 MeV protons as well as MeV electrons emitted by 90Sr. The charge collection efficiency (CCE) dependence on voltage evaluated using 4.5 MeV protons in the ±100 V range saturates at around 92±2% at 100 V, while coincidence experiments with MeV electrons confirmed that the whole pillars length is active in collecting the charge carriers. The mapping of CCE spatial distribution with an ion beam induced current technique showed that only a narrow (a few microns) damaged zone around the graphite electrodes has a reduced CCE, while the main diamond volume preserves excellent detection properties