We present experimental results and numerical Finite Element analysis to describe surface swelling due to the creation of buried graphite-like inclusions in diamond substrates subjected to MeV ion implantation. Numerical predictions are compared to experimental data for MeV proton and helium implantations, performed with scanning ion microbeams. Swelling values are measured with white light interferometric profilometry in both cases. Simulations are based on a model which accounts for the through-the-thickness variation of mechanical parameters in the material, as a function of ion type, fluence and energy. Surface deformation profiles and internal stress distributions are analyzed and numerical results are seen to adequately fit experimental data. Results allow us to draw conclusions on structural damage mechanisms in diamond for different MeV ion implantations.Comment: 15 pages, 4 figure

An accurate control of the optical properties of single crystal diamond during microfabrication processes such as ion implantation plays a crucial role in the engineering of integrated photonic devices. In this work we present a systematic study of the variation of both real and imaginary parts of the refractive index of single crystal diamond, when damaged with 2 and 3 MeV protons at low-medium fluences (range: 10 15 -10 17 cm 2 ). After implanting in 125 × 125 μm 2 areas with a scanning ion microbeam, the variation of optical pathlength of the implanted regions was measured with laser interferometric microscopy, while their optical transmission was studied using a spectrometric set-up with micrometric spatial resolution. On the basis of a model taking into account the strongly non-uniform damage profile in the bulk sample, the variation of the complex refractive index as a function of damage density was evaluated. ©2012 Optical Society of America

We present experimental results and numerical simulations to investigate the modification of structural-mechanical properties of ion-implanted single-crystal diamond.A phenomenological model is used to derive an analytical expression for the variation of mass density and elastic properties as a function of damage density in the crystal. These relations are applied together with SRIM Monte Carlo simulations to set up Finite Element simulations for the determination of internal strains and surface deformation of MeV-ion-implanted diamond samples. The results are validated through comparison with high resolution X-ray diffraction and white-light interferometric profilometry experiments. The former are carried out on 180 keV B implanted diamond samples, to determine the induced structural variation, in terms of lattice spacing and disorder, whilst the latter are performed on 1.8 MeV He implanted diamond samples to measure surface swelling. The effect of thermal processing on the evolution of the structural-mechanical properties of damaged diamond is also evaluated by performing the same profilometric measurements after annealing at 1000 °C, and modeling the obtained trends with a suitably modified analytical model. The results allow the development of a coherent model describing the effects of MeV-ion-induced damage on the structural-mechanical properties of single-crystal diamond. In particular, we suggest a more reliable method to determine the sofor the considered implantation type.

We have constructed and tested a custom-made magnetic-imaging-compatible visual projection system designed to project on a very wide visual field (~80°). A standard projector was modified with a coupling lens, projecting images into the termination of an image fiber. The other termination of the fiber was placed in the 3-T scanner room with a projection lens, which projected the images relayed by the fiber onto a screen over the head coil, viewed by a participant wearing magnifying goggles. To validate the system, widefield stimuli were presented in order to identify retinotopic visual areas. The results showed that this low-cost and versatile optical system may be a valuable tool to map visual areas in the brain that process peripheral receptive fields.Keywords Wide-field retinotopy . fMRI . Visual projection system Functional magnetic resonance imaging (fMRI) is currently one of the most widely used noninvasive techniques for measuring local neural activity. Most fMRI studies involve projecting visual stimuli using magnet-safe liquid crystal display or projectors equipped with custom optics that allow the delineation of visual brain areas. However, these techniques are compromised by their narrow fields of view (<30 deg), thus limiting studies of the visual system to the central visual field. Consequently, the study of peripheral vision in both healthy and clinical human subjects, as well as the essential preoperative mapping of the entire visual field in associative cortices, is impossible with most projection systems available at present.Two different types of 2-D visual stimulus presentation systems have been developed in the past. The first system (Roby, Gao, & Fox, 2000) is based on back-projection and comprises an LCD projector with a modified lens (located outside the scanner room), a custom lens, a rear-projection screen, and an adjustable folding mirror. The last two components are mounted on the head coil of the scanner. The custom lens images the LCD of the projector on the rear-projection screen, and the participant views the stimuli on the screen through the adjustable folding mirror. The resulting field of view is 26 × 56 deg. The second type, devised by Cornelissen, Pelli, Farell, and Huckins (1997) is based on a fiberscope. It comprises an LCD located outside the scanner room, the image fiber into which an objective lens projects, and an eyepiece through which the other end of the image fiber projects, thus allowing the participant to view the stimuli. The field of view achieved in this case is still limited, only 28 × 35 deg.In an attempt to increase the field of view, Pitzalis et al. (2006) implemented a few changes to a Btraditional^visual presentation system. They used a custom head coil in a 1.5-T Siemens Vision MR scanner (Siemens Medical Systems, Erlangen, Germany), which could accommodate a 260 × 185 mm back-projection screen. This screen was placed in the scanner at a distance of 100-120 mm from the participant's eyes and was viewed directly, rather than via a folding mirror, ...

Cases of long-term deformation of fused silica glass at room temperature attributed to the action of gravity have been reported. Further experimental investigations now provide evidence of time-dependent viscous behavior, with a time constant of the order of 10 years. Data relating to a pair of fused silica reference plates are presented, showing the overall deformation occurred over the years; considerations on the pertaining viscosity with aging are also given. An account of the observed relaxation process in terms of the Kelvin-Voigt model for linear viscoelasticity is provided.