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Pollen records from perennially frozen sequences provide vegetation and climate reconstruction for the last 48,000 14C years in the central part of Taymyr Peninsula. Open larch forest with Alnus fruticosa and Betula nana grew during the Kargin (Middle Weichselian) Interstade, ca. 48,000–25,000 14C yr B.P. The climate was generally warmer and wetter than today. Open steppe-like communities with Artemisia, Poaceae, Asteraceae, and herb tundralike communities with dwarf Betula and Salix dominated during the Sartan (Late Weichselian) Stade, ca. 24,000–10,300 14C yr B.P. The statistical information method used for climate reconstruction shows that the coldest climate was ca. 20,000–17,000 14C yr B.P. A warming (Allerød Interstade?) with mean July temperature ca. 1.5°C warmer than today occurred ca. 12,000 14C yr B.P. The following cooling with temperatures about 3°–4°C cooler than present and precipitation about 100 mm lower corresponds well with the Younger Dryas Stade. Tundra–steppe vegetation changed to Betula nana–Alnus fruticosa shrub tundra ca. 10,000 14C yr B.P. Larch appeared in the area ca. 9400 14C yr B.P. and disappeared after 2900 14C yr B.P. Cooling events ca. 10,500, 9600, and 8200 14C yr B.P. characterized the first half of the Holocene. A significant warming occurred ca. 8500 14C yr B.P., but the Holocene temperature maximum was at about 6000–4500 14C yr B.P. The vegetation cover approximated modern conditions ca. 2800 14C yr B.P. Late Holocene warming events occurred at ca. 3500, 2000, and 1000 14C yr B.P. A cooling (Little Ice Age?) took place between 500 and 200 14C yr ago.
We have studied the structure and growth regularities of highly ordered para-sexiphenyl (C36H26) thin films deposited by Hot Wall Epitaxy on mica. In particular, atomic force microscopy (AFM) was used to investigate the early growth stage of these films, in order to find the process controlling parameters. It was shown that the substrate temperature and the growth time are important parameters for control of the film morphology, in terms of the degree of anisotropy and long range order. X-ray diffraction pole figure technique and transmission electron microscopy were also used to characterize the crystallographic structure of the thicker films. We have shown that the highly ordered crystallites of para-sexiphenyl (showing needle-like morphology by AFM) are oriented with their (11 1 ) or (11 2 ) crystallographic planes parallel to the substrate surface. For each of these two orientations there are two opposite directions for growth of crystallites reflecting the two-fold symmetry of the mica surface.
This work focuses on single - and bilayers of para - hexaphenyl (PHP) and C60 grown by Hot Wall Epitaxy. A detailed study of the growth process was performed on glass, ITO and (001)- oriented cleaved mica substrates. The ordering of the layers was investigated by X-ray diffraction, showing clear diffraction peaks for layers grown on mica. The PHP layers grown on mica show high optical anisotropy (dichroic ratios up to 14 in emission) according to the polarization dependent photoluminescence experiments. The highly ordered structure is also reflected in the surface morphology of the layer as observed by atomic force microscopy. The epitaxial growth on mica is mirrored by the main alignment of the surface structure to the orientation of the mica substrate.
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