Picosecond-laser-induced structural modifications in the bulk of single-crystal diamond

Arrays of through laser-graphitized microstructureshavebeenfabricatedintypeIIasingle-crystal1.2-mmthick diamond plates by multipulse laser irradiation with 10-ps pulses at λ=532 nm wavelength. Raman and photoluminescence (PL) spectroscopy studies of the bulk microstructures have evidenced the diamond transformation to amorphous carbon and graphitic phases and the formation of radiation defects pronounced in the PL spectra as the self-interstitial related center, the 3H center, at 504 nm. It is found that the ultrafast-laser-induced structural modifications in the bulk of single-crystal diamond plates occur along{111}planes, known as the planes of the lowest cleavage energy and strength in diamond

Probing the Nanostructure of Neutron-Irradiated Diamond Using Raman Spectroscopy

Disordering of crystal lattice induced by irradiation with fast neutrons and other high-energy particles is used for the deep modification of electrical and optical properties of diamonds via significant nanoscale restructuring and defects engineering. Raman spectroscopy was employed to investigate the nature of radiation damage below the critical graphitization level created when chemical vapor deposition and natural diamonds are irradiated by fast neutrons with fluencies from 1 × 1018 to 3 × 1020 cm−2 and annealed at the 100–1700 °C range. The significant changes in the diamond Raman spectra versus the neutron-irradiated conditions are associated with the formation of intrinsic irradiation-induced defects that do not completely destroy the crystalline feature but decrease the phonon coherence length as the neutron dose increases. It was shown that the Raman spectrum of radiation-damaged diamonds is determined by the phonon confinement effect and that the boson peak is present in the Raman spectra up to annealing at 800–1000 °C. Three groups of defect-induced bands (first group = 260, 495, and 730 cm−1; second group = 230, 500, 530, 685, and 760 cm–1; and third group = 335, 1390, 1415, and 1740 cm−1) were observed in Raman spectra of fast-neutron-irradiated diamonds

Raman Study of the Diamond to Graphite Transition Induced by the Single Femtosecond Laser Pulse on the (111) Face

The use of the ultrafast pulse is the current trend in laser processing many materials, including diamonds. Recently, the orientation of the irradiated crystal face was shown to play a crucial role in the diamond to graphite transition process. Here, we develop this approach and explore the nanostructure of the sp2 phase, and the structural perfection of the graphite produced. The single pulse of the third harmonic of a Ti:sapphire laser (100 fs, 266 nm) was used to study the process of producing highly oriented graphite (HOG) layers on the (111) surface of a diamond monocrystal. The laser fluence dependence on ablated crater depth was analyzed, and three different regimes of laser-induced diamond graphitization are discussed, namely: nonablative graphitization, customary ablative graphitization, and bulk graphitization. The structure of the graphitized material was investigated by confocal Raman spectroscopy. A clear correlation was found between laser ablation regimes and sp2 phase structure. The main types of structural defects that disrupt the HOG formation both at low and high laser fluencies were determined by Raman spectroscopy. The patterns revealed give optimal laser fluence for the production of perfect graphite spots on the diamond surface

IR Spectroscopy of Vacancy Clusters (Amber Centers) in CVD Diamonds Nanostructured by Fast Neutron Irradiation

We investigated the IR absorption spectra of CVD diamond damaged by fast neutrons (>0.1 MeV) with high fluences ranging from 1 × 1018 to 2 × 1019 cm−2 and annealed at temperatures of 200 °C to 1680 °C. After annealing above 1000 °C, the formation of “amber-centers” (ACs), associated with multivacancy clusters, is detected as deduced from the appearance of a strong absorption line at 4100 cm−1. Moreover, the concentration of the ACs in the irradiated diamond can be an order of magnitude higher than that observed previously in the darkest brown natural diamonds. A number of other absorption lines, including the H1b center at 4936 cm−1 (0.612 eV) and new lines at ~5700 cm−1 (0.706 eV) and 9320 cm−1 (1.155 eV) not reported before in the literature, are observed, and their intensity evolutions at annealing temperatures are documented. At the highest fluences, all the lines show reduced intensities and broadening and spectral shifts due to a very high defect concentration and partial amorphization. The obtained experimental data can be used for the analysis of defect generation, transformations and healing in irradiated synthetic and natural diamonds

Nano-carbon pixels array for ionizing particles monitoring

The paper deals on the response of a polycrystalline diamond sensor, 500 μm thick, to particles from a 90Sr β-source. 21×21 nano-carbon pads, with 0.18 mm×0.18 mm area each, were realized by ArF excimer laser irradiation on one diamond face, whereas a 7×7 mm2 backside contact was fabricated and used for sensor biasing during characterization of sensor under β-source irradiation. The carbon pads embrace a number of grains, which show different degrees of surface graphitization dependent on the grain orientations. Each carbon pad exhibits a linear I(V) response up to 200 V. The average number of charge carriers collected by a single pixel, as well as the distribution of pixels involved by the impinging particle tracking, is analyzed as a function of the applied voltage recording the signals acquired by 16 pixels at a time. The pulse height distribution is not affected by reversing the bias polarity. For a single pixel, the most probable collected charge value is 1.40±0.02 fC whereas the main value gives coll=1.67±0.02 fC (10430 ±120 electrons). The charge collection distance was measured tacking into account the effect induced by high- energy electrons and found to be 285±3 μm, demonstrating the absence of bulk defects induced by the laser graphitization processing. Cross-talk effects between nearest-neighbor pixels has been excluded analyzing the results obtained in a batch of more than 1000 events even if the same cannot be excluded under higher energy particles

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)