[en] Optical absorption (OA) and electron spin resonance measurements have been performed on IIa, Ib, IaA and IaB type diamonds irradiated by 3 MeV electrons. OA reveals that the GR1 system in diamond is usually accompanied by an underlying broad background band, which is tentatively attributed to strained neutral vacancies (V deg. ). The photochromic changes in OA suggest that the concentration calibration constants for the V deg. , H3 and H4 defects should be halved, that the 3H and 5RL centres could be different charge states of a di-interstitial related defect and that the di-interstitial R1, 3H and 5RL centres in diamond are stable to annealing temperatures up to at least 800 deg. C. The generation and annealing of interstitials and vacancies have been studied as a function of the nitrogen concentration and aggregation state. The results suggest that single substitutional nitrogen (N_S) efficiently traps carbon interstitials, but releases them upon annealing at 400 deg. C. Defects related to nitrogen aggregation in IaB diamond also trap interstitials, but do not release them upon annealing. Carbon interstitials are not trapped by N_S-N_S pairs. Instead, an increase in the concentration of N_S-N_S centres enhances the production rates of vacancies and interstitials, reduces their annealing temperatures and favours formation of the 3H over R1 di-interstitials

[en] The W27 centre has been characterized by means of electron spin resonance in natural diamond. The centre exhibits spin S=1, a large spin-spin coupling constant D=99 mT, and a complex hyperfine interaction structure interpreted as originating from interaction of an S=1 electronic system with five nitrogen atoms: two of these sites are equivalent and are located near the S = 1 electrons; three others are nearly equivalent and more remote. The centre is suggested to include a divacancy, where one vacancy, bound to two nitrogen atoms and one carbon atom, has trapped an extra electron, while the second vacancy is bound to three substitutional nitrogen atoms

[en] An undocumented photoluminescence centre at 1.789 eV has been characterized in diamonds grown by a high-pressure high-temperature technique. It could only be observed in nitrogen-free crystals grown in a Fe-containing chamber. The centre is unique for diamond due to its room-temperature linewidth, which can be as small as 1 meV. Polarization, temperature and time-resolved measurements reveal that the corresponding defect has trigonal symmetry, a 3.7 meV splitting in the ground state, vibronic modes of 30 and 48 meV, very weak electron-phonon coupling and a lifetime of 7 ms at room temperature. The centre is attributed to an interstitial Fe related defect. (author). Letter-to-the-editor

[en] This work discusses the current situation in the study of bulk defects in diamond, grown by chemical vapour deposition (CVD), using optical absorption, luminescence, and electron spin resonance techniques. CVD diamond appears distinct from other types of diamond in that it exhibits significant concentrations of bulk defects involving hydrogen, silicon, and possibly tungsten impurities. Importantly, as regards doping, p-type conductivity up to the degeneracy level can be achieved by boron incorporation, while n-type conductivity can be realized by phosphorus doping. A generally observed trend is cross fertilization between the studies of various types of diamond: the knowledge of the properties of intrinsic and irradiation-induced defects, obtained from extensive studies of natural and high-pressure synthetic diamond crystals, helps in understanding the presence of certain radiation-damage-related centres in as-grown CVD films. In return, some achievements from the study of defect centres in CVD diamond may provide useful information for modelling of defects in crystalline diamond and other semiconducting materials. (author)

[en] We have studied the damage induced by 80 keV Er implantation in epitaxial GaN/sapphire layers at room temperature and at 450 deg. C. The dopant distribution and lattice damage were investigated using Rutherford backscattering, channeling spectrometry and X-ray diffraction, whereas photoluminescence was used to probe the optical response. Random implantation results in substantial damage accumulation, which is difficult to recover during subsequent annealing. To reduce the ion-induced damage, we applied channeled implantation, i.e. directing the Er-beam along the nitride c-axis. Using this implantation geometry, a drastic decrease in the induced damage is observed. Channeled implantation generally results in green luminescence lines at room temperature, whereas no Er-related luminescence is observed after random implantation

[en] An extensive study of Co- and Ni-related centres in high-pressure synthetic diamond, using electron spin resonance, optical absorption and luminescence techniques, has revealed that most of these defects, in samples grown at low temperature (∼ 1400 deg. C), exhibit preferential alignment, i.e. a non-equal distribution over crystallographically equivalent orientations. Remarkably, this observation applies not only to defects assumed to involve only an Ni or a Co atom, but also to some Ni-N complexes. Annealing at T>1600 deg. C induces nitrogen mobility and the corresponding formation of numerous Ni-N- and Co-N-related centres. This annealing eventually destroys the preferential polarization of low-temperature centres

[en] Synthetic boron-doped single-crystal diamonds were irradiated by a pulsed electron beam at 2.2 MeV to various accumulated fluences from 0.7 x 10¹⁸ to 10 x 10¹⁸ e^- cm^-2. The samples were then subjected to isochronal annealing up to 1260 deg. C and characterized by positron annihilation (PA) and optical absorption (OA) spectroscopies after each annealing step. PA combined with in situ monochromatic illumination gave an estimate for the positive/neutral energy level in the band gap for the monovacancy as ∼0.6 eV above the valence band-edge. From the analysis of PA and OA results, a dominant OA line at 0.552 eV was associated with a neutral boron-interstitial complex, and the annealing temperature of the positive monovacancy was deduced as ∼700 deg. C

[en] The structure of individual nanodiamond grains produced by the detonation of carbon-based explosives has been studied with a high-vacuum aberration-corrected electron microscope. Many grains show a well-resolved cubic diamond lattice with negligible contamination, thereby demonstrating that the non-diamond shell, universally observed on nanodiamond particles, could be intrinsic to the preparation process rather than to the nanosized diamond itself. The strength of the adhesion between the nanodiamond grains, and the possibility of their patterning with sub-nanometer precision, are also demonstrated

[en] Recently, a novel form of nanodiamond exhibiting unusual mechanical properties has been synthesized by high-pressure high-temperature (HPHT) treatment of C₆₀ fullerene, amorphous carbon and diamond powder. In this study, we have characterized the dominant defects in this nanodiamond by a combination of optical absorption, luminescence, Raman, electron spin resonance and elastic recoil detection techniques. Unusually high concentrations (∼0.4 at.%) of hydrogen and very low concentrations of nitrogen (∼10^-5 at.%) have been detected in diamond grown from C₆₀. Although most of hydrogen is shown to originate from inclusions of foreign phases, such as water, significant concentrations (∼0.01 at.%) of hydrogen were also detected as a point defect in the nanodiamond grains. Observed structural differences between the samples made from various carbonaceous materials are attributed to different behaviour of the starting compounds during HPHT treatment. (letter to the editor)

[en] A large number (>60) of nitrogen-containing type Ia natural diamonds, and nitrogen-free type IIa natural and synthetic diamonds, have been electron irradiated and their optical absorption spectra have been analysed in detail. The analysis reveals that the concentrations of vacancies [V] and interstitials [I⁰ ] in type IaA diamonds increase linearly with the concentration [N_A ] of the A-form of nitrogen. This increase of [V] and [I⁰] with [N_A ] is attributed to the trapping of vacancies and interstitials in the strain field of nitrogen. The trapping produces 'strained' vacancies and partly immobilizes interstitials, thus reducing the vacancy-interstitial recombination during electron irradiation, thereby increasing [V] and [I⁰ ]. Those strained vacancies and interstitials recombine upon annealing at temperatures ∼390-420 deg. C. In type IaB diamonds no correlation has been found between [V] and the concentration [N_B ] of the B-form of nitrogen; furthermore [I⁰] was found to decrease linearly with [N_B ]. In both type IaA and type IaB diamonds the width of the GR1 zero-phonon line, associated with the neutral vacancies [V⁰ ], increases with nitrogen concentration. A new, more appropriate and accurate formula to calculate [V⁰] is proposed based on measuring the height H of the GR1 absorption band at 2.0 eV