A palaeoenvironmental reconstruction of the Middle Jurassic of Sardinia (Italy) based on integrated palaeobotanical, palynological and lithofacies data assessment

During the Jurassic, Sardinia was close to continental Europe. Emerged lands started from a single island forming in time a progressively sinking archipelago. This complex palaeogeographic situation gave origin to a diverse landscape with a variety of habitats. Collection- and literature-based palaeobotanical, palynological and lithofacies studies were carried out on the Genna Selole Formation for palaeoenvironmental interpretations. They evidence a generally warm and humid climate, affected occasionally by drier periods. Several distinct ecosystems can be discerned in this climate, including alluvial fans with braided streams (Laconi-Gadoni lithofacies), paralic swamps and coasts (Nurri-Escalaplano lithofacies), and lagoons and shallow marine environments (Ussassai-Perdasdefogu lithofacies). The non-marine environments were covered by extensive lowland and a reduced coastal and tidally influenced environment. Both the river and the upland/hinterland environments are of limited impact for the reconstruction. The difference between the composition of the palynological and palaeobotanical associations evidence the discrepancies obtained using only one of those proxies. The macroremains reflect the local palaeoenvironments better, although subjected to a transport bias (e.g. missing upland elements and delicate organs), whereas the palynomorphs permit to reconstruct the regional palaeoclimate. Considering that the flora of Sardinia is the southernmost of all Middle Jurassic European floras, this multidisciplinary study increases our understanding of the terrestrial environments during that period of time

Crack-free interface in wafer-bonded Ge/Si by patterned grooves

Crack-free Interfaces can be achieved in wafer-bonded Ge/Si by using Patterned grooves Using synchrotron radiation phase-contrast Imaging and scanning electron microscopy, we observed cracking that is Induced by thermal stresses in thin (h(Ge) <= 0 5h(Si)) Ge wafers on smooth Si substrates Theoretical calculation shows it remarkable reduction in thermal stresses in Ge wafer bonded to grooved Si substrate We demonstrate the fabrication of crack-free Ge/Si (h(Ge) = 0 5h(Si)) structure by patterned grooves, its confirmed by in ohmic I-V characteristic across the heterojunction (C) 2009 Acta Materialia Inc Published by Elsevier Ltd All rights reservedX1122sciescopu

Direct bonding of silicon carbide wafers with a regular relief at the interface

The direct bonding of two oxide-free 6H-SiC(0001) silicon carbide single crystal wafers, one smooth and another bearing an artificial microscopic relief, has been studied. According to the X-ray topography data, the bonded surface fraction reaches 85% of the total area. The pattern of stress distribution at the interface is aperiodic, which is indicative of an inhomogeneous microroughness of the surface of bonded wafers.X117sciescopu

Structural and Electrical Properties of SiGe-on-Insulator Substrates Fabricated by Direct Bonding

A new method for fabricating SiGe-on-insulator substrates, i.e., direct bonding of thermally oxidized Si wafers with Si(1-x)Ge(x) wafers cut from Czochralski-grown crystals, is suggested. Si(1-x)Ge(x) layers no larger than 10 mu m thick in SiGe/SiO(2)/Si compositions were fabricated by chemical mechanical polishing. To increase the Ge content in the Si(1-x)Ge(x) layer, thermal oxidation was used. It was shown that the increase in the Ge content and heat treatment procedures at 1250 degrees C are not accompanied by degradation of structural and electrical characteristics of Si(1-x)Ge(x) layers.X1111sciescopu

White X-ray beam topography and radiography of Si1-xGex crystals bonded to silicon

The defect structure of Si1-xGex. wafers with 4% of germanium and their interfaces with Si wafers were studied using white radiation topography and phase-sensitive radiography. The heterostructures were manufactured by direct bonding of Si1-xGex. and Si crystalline wafers made of bulk crystals that were grown by the Czochralski technique. In Si1-xGex. crystals, the segregations of Ge act as dislocation nucleation sites. In Si1-xGex/Si bonded structures, the segregation of Ge as well as the accumulation of dislocations induce elastic strain and plastic deformation during high-temperature bonding annealing. With the topography-radiography combination, we are able not only to detect microcracks, indicating nonbonded areas, by radiography, but also to reveal dislocations and long-range strain fields by topography at the same time. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.X114sciescopu

Structural and electrical properties of the GexSi1-x/Si heterojunctions obtained by the method of direct bonding

The results of studying the structural and electrical properties of structures produced by the method of direct bonding of GexSi1-x and Si wafers are reported. The wafers were cut from the crystals grown by the Czochralski method. Continuity of the interface and the crystal-lattice defects were studied by X-ray methods using synchrotron radiation and by scanning electron microscopy. Measurements of the forward and reverse current-voltage characteristics of the p-GexSi1-x /n-Si diodes made it possible to assess the effect of the crystallattice defects on the electrical properties of heterojunctions. Satisfactory electrical parameters suggest that the technology of direct bonding is promising for the fabrication of large-area GexSi1-x /Si heterojunctions.X114sciescopu

Current-voltage characteristics of Si/Si1-x Ge (x) heterodiodes fabricated by direct bonding

We have studied the current-voltage (I-U) characteristics of Si/Si1 - x Ge (x) (0.02 < x < 0.15) heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si1 - x Ge (x) wafers of the same orientation containing 2-15 at % Ge. An increase in the germanium concentration N (Ge) in Si1 - x Ge (x) crystals is accompanied by a growth in the density of crystal lattice defects, which leads to a decrease in the minority carrier lifetime in the base of the heterodiode and an increase in the recombination component of the forward current and in the differential resistance (slope) of the I-U curve. However, for all samples with N (Ge) a parts per thousand currency sign 15 at %, the I-U curves of Si/Si1 - x Ge (x) heterodiodes are satisfactory in the entire range of current densities (1 mA/cm(2)-200 A/cm(2)). This result shows good prospects for using direct bonding technology in the fabrication of Si/Si1 - x Ge (x) heterostructures.X1142sciescopu