Acoustic wave studies during fast ion beam interactions with solds

Ion beam material modification is currently being used for several important technological applications such as semiconductor doping [1], surface modification of metals [2], cold etching [1], micro machining [1] and material analysis [3]. Ion beam processing has many advantages [4]. The speed, homogeneity and reproducibility of the doping process are easily controlled. Tight control of the number of doping atoms is possible. Low purity dopants can be used. The target can be kept at low temperatures allowing for low melting temperature materials to be modified. Simple masking methods can be employed and doping can be performed through passive films. Low penetration depths can be achieved and multiple implantations can produce varied doping profiles. Devices with small dimensions can be manufactured due to the small size of the ion beam. Since ion implantation is not an equilibrium process, equilibrium solubility limits of the ion species in the target material can be exceeded. There are some disadvantages of this type of doping process. Damage is caused to the crystal structure creating defects. Implantation is limited to near-surface regions and theoretical profiles can be difficult to obtain due to effects of channeling and diffusion [5]

The Iceland Microcontinent and a continental Greenland-Iceland-Faroe Ridge

The breakup of Laurasia to form the Northeast Atlantic Realm was the culmination of a long period of tectonic unrest extending back to the Late Palaeozoic. Breakup was prolonged and complex and disintegrated an inhomogeneous collage of cratons sutured by cross-cutting orogens. Volcanic rifted margins formed, which are blanketed by lavas and underlain variously by magma-inflated, extended continental crust and mafic high-velocity lower crust of ambiguous and probably partly continental provenance. New rifts formed by diachronous propagation along old zones of weakness. North of the Greenland-Iceland-Faroe Ridge the newly forming rift propagated south along the Caledonian suture. South of the Greenland-Iceland-Faroe Ridge it propagated north through the North Atlantic Craton along an axis displaced ~ 150 km to the west of the northern rift. Both propagators stalled where the confluence of the Nagssugtoqidian and Caledonian orogens formed a transverse barrier. Thereafter, the ~ 400-km-wide latitudinal zone between the stalled rift tips extended in a distributed, unstable manner along multiple axes of extension that frequently migrated or jumped laterally with shearing occurring between them in diffuse transfer zones. This style of deformation continues to the present day. It is the surface expression of underlying magma-assisted stretching of ductile mid- and lower continental crust which comprises the Icelandic-type lower crust that underlies the Greenland-Iceland-Faroe Ridge. This, and probably also one or more full-crustal-thickness microcontinents incorporated in the Ridge, are capped by surface lavas. The Greenland-Iceland-Faroe Ridge thus has a similar structure to some zones of seaward-dipping reflectors. The contemporaneous melt layer corresponds to the 3–10 km thick Icelandic-type upper crust plus magma emplaced in the ~ 10–30-km-thick Icelandic-type lower crust. This model can account for seismic and gravity data that are inconsistent with a gabbroic composition for Icelandic-type lower crust, and petrological data that show no reasonable temperature or source composition could generate the full ~ 40-km thickness of Icelandic-type crust observed. Numerical modeling confirms that extension of the continental crust can continue for many tens of Myr by lower-crustal flow from beneath the adjacent continents. Petrological estimates of the maximum potential temperature of the source of Icelandic lavas are up to 1450 °C, no more than ~ 100 °C hotter than MORB source. The geochemistry is compatible with a source comprising hydrous peridotite/pyroxenite with a component of continental mid- and lower crust. The fusible petrology, high source volatile contents, and frequent formation of new rifts can account for the true ~ 15–20 km melt thickness at the moderate temperatures observed. A continuous swathe of magma-inflated continental material beneath the 1200-km-wide Greenland-Iceland-Faroe Ridge implies that full continental breakup has not yet occurred at this latitude. Ongoing tectonic instability on the Ridge is manifest in long-term tectonic disequilibrium on the adjacent rifted margins and on the Reykjanes Ridge, where southerly migrating propagators that initiate at Iceland are associated with diachronous swathes of unusually thick oceanic crust. Magmatic volumes in the NE Atlantic Realm have likely been overestimated and the concept of a monogenetic North Atlantic Igneous Province needs to be reappraised. A model of complex, piecemeal breakup controlled by pre-existing structures that produces anomalous volcanism at barriers to rift propagation and distributes continental material in the growing oceans fits other oceanic regions including the Davis Strait and the South Atlantic and West Indian oceans

Acoustic wave studies during fast ion beam interactions with solds

Ion beam material modification is currently being used for several important technological applications such as semiconductor doping [1], surface modification of metals [2], cold etching [1], micro machining [1] and material analysis [3]. Ion beam processing has many advantages [4]. The speed, homogeneity and reproducibility of the doping process are easily controlled. Tight control of the number of doping atoms is possible. Low purity dopants can be used. The target can be kept at low temperatures allowing for low melting temperature materials to be modified. Simple masking methods can be employed and doping can be performed through passive films. Low penetration depths can be achieved and multiple implantations can produce varied doping profiles. Devices with small dimensions can be manufactured due to the small size of the ion beam. Since ion implantation is not an equilibrium process, equilibrium solubility limits of the ion species in the target material can be exceeded. There are some disadvantages of this type of doping process. Damage is caused to the crystal structure creating defects. Implantation is limited to near-surface regions and theoretical profiles can be difficult to obtain due to effects of channeling and diffusion [5].</p