Micro-Raman spectroscopy of near-surface damage in diamond irradiated with 9-MeV boron ions

Abstract

We have studied the near-surface damage in a diamond crystal caused by irradiation with swift boron ions and its healing after high-temperature annealing. A diamond crystal was irradiated with 9-MeV 11 B 3+ ions with fluence values between 1 × 10 15 and 4.42 × 10 16 ions/cm 2 to generate various levels of lattice damage. The ions loose energy to the lattice and, according to simulations, stop at a depth of about 5 µm, where they form a thin buried implantation layer. For the near-surface layers damage is produced by the ions at high kinetic energy before they slow down. Only intrinsic defects can be produced, with no boron atoms. The lattice damage of the near-surface layers and its recovery after annealing for 1 hour at 1000 • C were studied by Raman and photoluminescence spectroscopies. Back-scattered light from a 514.5-nm laser beam was collected from the sample surface, probing a depth of a few micrometers. We observe some disordering of the lattice plus the formation of neutral vacancies, interstitial and other lattice defects. After annealing the Raman spectrum shows a significant recovery of the lattice order and the disappearance of isolated neutral vacancies. Residual damage is confirmed by the luminescence spectrum, that shows the appearance of new spectral features.

Lattice damage in 9-MeV-carbon irradiated diamond and its recovery after annealing

“…The second peak at 1627 cm −1 is due to the dumbbell defect or 100 split interstitial defect, which consists of an isolated double bonded (sp 2 ) carbon pair in a carbon site [27]. We have observed the same peaks for the near surface layers in 9-MeV-boron irradiated diamond [37]. These peaks disappear after annealing, indicating that the diffusion of atoms removes most vacancies and interstitial defects produced upon irradiation.…”

“…The position of the peak is reduced upon irradiation, reaching a minimum for the stopping layer. This correlates with the increase in the width, following the relationship between width and position due to the anharmonic decay of the optical one-phonon into two acoustic phonons [27,37,41], induced by the increasing disorder of the diamond lattice upon irradiation. After annealing there is an important recovery of the lattice except for fluences around 130 × 10 14 ions/cm 2 , for which no recovery is possible.…”

“…The increasing disorder is also evidenced by the widening of the peak with fluence at the irradiated layers and, specially, at the stopping layer. Note, however, that the broadening is still very important for the near-surface and intermediate layers, reflecting also a significant damage for these layers [37]. It also shows that Raman spectroscopy is very sensitive to lattice damage of 10 21 vacancies/cm 3 .…”

“…We have shown before [37] that when a wavelength of 514.5 nm (2.41 eV) is used for excitation, not far from the Raman bands one can observe also photoluminescence bands. These bands are more sensitive than the Raman peaks to the residual damage after annealing [37]. We have measured the photoluminescence spectra of the irradiated zones in the photon energy range between 1.4 and 2.4 eV, as a function of irradiation fluence and layer depth.…”

“…Raman spectroscopy has been extensively used to monitor the damage and the transformation of the diamond lattice after ion irradiation [24,25,27,29,[32][33][34][35][36][37]. Combined Raman and photoluminescence spectroscopy are very sensitive to the residual damage, as shown in our previous paper [37]. In that paper we irradiated diamond with 9 MeV boron ions.…”