A metamaterial consisting of periodic regions of high electrical conductivity in a 3 × 3 × 1.5 mm synthetic-diamond crystal has been fabricated by researchers at Kyoto University (Kyoto, Japan); the regions are created by focusing 230 fs pulses at 1 kHz from a modelocked Ti:sapphire laser to a beam-waist diameter of 2 µm and an energy fluence of 28.5 J/cm2 within the crystal. Testing the structure involved ablating the diamond surface to 23 µm deep with a focused-ion beam and then measuring with scanning-electron microscopy and micro-Raman spectroscopy.
Results showed that at a scanning speed of 20 µm/s, the ablated areas were transformed to a form of carbon that had an electrical conductivity of up to 64 S/m (this compares to crystalline graphite at about 104 S/m and amorphous carbon at about 10-2 S/m). The tests indicate that the change occurs due to a reduction of bond-angle disorder at sp2 aromatic rings, causing graphitization of the diamond structure. Scanning the laser spot at lower speeds caused recrystallization into diamond, with reduced conductivity. Potential uses of the metallo-dielectric photonic crystal include wire-grid polarizers and terahertz metamaterials. Contact Yasuhiko Shimotsuma at [email protected].
