T.E. Derry

Radiation defects and their annealing behaviour in ion-implanted diamonds

Abstract The major studies, in our laboratories, which led to a model of defect creation and annealing during ion implantation into diamond, are discussed. From the data that have been gathered, the radiation-defect processes are consistent with simple vacancy–interstitial atom creation in the collision cascades. Accordingly, it has been assumed that, owing to its high radiation hardness, displacement spikes do not play an important role in the generation of defects in diamond. The point defects that are created can migrate by diffusion at suitable temperatures. Diffusing self-interstitial atoms can either meet up with vacancies and annihilate them, or diffuse out of the layer being implanted (or which had been implanted). The fraction that escapes before annihilating vacancies depends on the depth-width ω of the layer and the annealing temperature. With the aid of this model, two implantation-doping routines called cold-implantation-rapid-annealing (CIRA) and low-damage-drive-in (LODDI) have been devised. It is possible to generate p- and n-type layers in diamond using these routines, even when using keV implantations. From this theory, it is noted that MeV implantations should greatly increase the quality of the doped layers.

Depth profiling of implanted 13C in diamond as a function of implantation temperature

Abstract 13 C ions were implanted into natural type IIa diamond at temperatures ranging between that of liquid nitrogen and 670 K. Previous results [1] show that in the temperature range 320–670 K only the interstitials created in the damage cascade are mobile, the vacancies starting to diffuse only above these temperatures. The nuclear reaction 13 C(p, γ) 14 N was used to determine the depth distribution of the implanted 13 C atoms. Changes in the depth profiles as a function of implantation temperature reflected changes in mobility and trapping of the defects. All the depth profiles of diamonds implanted at temperatures greater than or equal to ambient temperature displayed a bimodal distribution consisting of the deeper than expected internal peak, and an overlapping surface peak. The integrated profile areas decreased with increasing implant temperature from 390 to 670 K. None of the sub-ambient implant temperature profiles showed a surface peak, but implantation done at 80 K displayed a strong tail extending deep into the diamond.

The production of defects and colloids in lithium fluoride crystals by implantation with rare gas ions

Optical absorption spectra in the range 2 eV to 12 eV are presented for lithium fluoride crystals implanted with rare gas ions argon and neon of energy 100 keV. F- and M-centres are produced by bot...

The redistribution of implanted atoms and radiation damage during the implantation doping of diamond

Abstract The dopant atoms 7 Li and 11 B were implanted into natural type Ia and type IIa diamond at temperatures ranging between 90 and 670 K. Nuclear reaction analysis was used to determine the depth distributions of the implanted dopants using the 165 keV 11 B(p, γ) 12 C resonance and the 441 keV 7 Li(p, γ) 8 Be resonance. Implants performed at 90 K were annealed at 360 K for 30 min and were then reprofiled to study the annealing characteristics of the dopants. In order to achieve optimum doping of diamond it is of importance to understand the damage processes that occur during low temperature (∼ 90 K) ion implantation, and their annealing at elevated temperatures. In order to do this, 13 C ions were implanted into natural type IIa diamond held at an implantation temperature of ∼ 90 K and profiled using the 550 keV 13 C(p, γ) N resonance, together with RBS channelling measurements made along the 〈 100 〉, 〈 110 〉, and 〈 111 〉 axes. This implant was then annealed at 670 K for 30 min and re-examined. The results indicate the presence of two defect regions in the implanted region: a near-surface region (extending to ∼ 0.25 μm) containing highly mobile single defects, and a deeper region (extending beyond the calculated ion range to ∼ 1.5 μm) containing more stable extended defects. The channelling results also show evidence for the possible hydrogenation of the damaged region.

Annealing studies on ion implanted diamond

Abstract In this study we report on an investigation of the degree of damage recovery after multi-implantation of 12C into diamond as a function of dose and annealing temperature. Three different doses spread over energies of 150, 120, 80 and 50 keV at an implantation temperature of −190°C were used: 5.25 × 1015, 2.9 × 1015 and 5.25 × 10 14 ions cm 2 . After the completion of each implantation the diamond was allowed to warm up to room temperature, whereupon ion channeling of 1.0 MeV protons was used to locate the three major diamond channels, the (100), (111) and (110). Finally 1.2 MeV He+ ions were then used to produce trans-axial scans of each channel to a depth of ~ 2700 A. The diamond was then annealed at 630, 1050, 1300 and finally 1500°C in an inert argon atmosphere. Channeling measurements on each of the axes were repeated after each anneal. The results indicate that damage removal is initiated from the surface, and advances progressively into the diamond as the annealing temperature is increased. The highest dose of 5 × 10 15 ions cm 2 introduces thermally stable defects into the damaged region which are not observed for the other implantation doses.

Volume expansion of diamond during ion implantation at low temperatures

A type IIa diamond was implanted with fluorine ions while being maintained at liquid nitrogen temperature (77 K). After allowing the diamond to warm to room temperature the volume expansion caused by the ion implantation was measured using standard profilometry. No expansion could be detected up to an ion dose 6×10 15 ions/cm 2 . Above this ion dose, expansion, which could be ascribed to amorphization of the ion damaged layer towards a graphite phase, did occur. This result is in severe contrast to ion implantation carried out above room temperature where expansion occurs immediately with the onset of ion implantation, and can be explained in terms of the diffusion of interstitials out of the ion damaged layer leaving behind a high density of immobile vacancies.

Ion beam studies of the static and dynamic properties of dopants in diamond

Abstract The exploitation of “point defect engineering” has recently enabled diamond to be doped artificially as a semiconductor for the first time, using boron ion implantation. Further progress requires more detailed knowledge of the distributions and lattice positions of the dopant atoms and defects, and their dynamical behaviour on annealing. Ion beam analysis has proved to be an ideal technique to investigate these phenomena, and some recent results are described, involving the dopants or potential dopants lithium, boron, nitrogen and fluorine. The importance of the nature and distribution of the radiation damage and of chemical effects in determining inward-outward migration and the stable resting sites of the different dopants are emphasized.

Analysis of the Indentation Size Effect in the Microhardness Measurements in B 6 O

The Vickers microhardness measurements of boron suboxide (B6O) ceramics prepared by uniaxial hot-pressing was investigated at indentation test loads in the range from 0.10 to 2.0 kgf. Results from the investigation indicate that the measured microhardness exhibits an indentation load dependence. Based on the results, we present a comprehensive model intercomparison study of indentation size effects (ISEs) in the microhardness measurements of hot-pressed B6O discussed using existing models, that is, the classical Meyers law, Li and Bradts proportional specimen resistance model (PSR), the modified proportional specimen resistance model (MPSR), and Carpinteris multifractal scaling law (MFSL). The best correlation between literature-cited load-independent Vickers microhardness values, the measured values, and applied models was achieved in the case of the MPSR and the MFSL models.

X-ray photoelectron spectroscopy of nitrogen-implanted cemented tungsten carbide (WC-Co)

In order to determine which compounds of cobalt formed during implantation, a nitrogen WC-Co sample was analysed by X-ray photoelectron spectroscopy (XPS)

The colouration of CaF 2 crystals by keV AND GeV ions

CaF 2 crystals have been implanted with a variety of ions of widely different energies and mass. Effects have been monitored using optical absorption in the range 120-750 v nm. This includes the vacuum UV region. For 100 v keV ions (Al, Mg, Kr) we observe extrinsic colloid bands in the case of implanted metal ions at high fluences (10 17 v ions v cm 2 ) but no colour centres (F, F 2 etc). For GeV ions (U, Ni) we observe prominent absorption bands in the visible region at fluences of 10 12 v ions v cm m 2 attributed to extrinsic calcium colloids. New optical features are discussed including an absorption band near 185 v nm in the VUV and bands at 604 v nm and 672 v nm in the visible region.