ABSTRACT:The early stage of spinodal decomposition of partially miscible poly(methyl methacrylate)/poly(styrene-co-acrylonitrile) blend was studied by time-resolved synchrotron radiation small-angle X-ray scattering (SR-SAXS). Intensity change of a scattering peak corresponding to the concentration fluctuation was traced after rapid heating to the two-phase region from the miscible state. At the initial stage, the dominant phase size was kept constant on the order of tens of nanometers, and then, grew to the order of sub-microns during decomposition. The apparent diffusion constant was determined according to the Cahn-Hilliard theory.KEY WORDS Spinodal Decomposition / Polymer Blend / Poly(methyl methacrylate) / Poly(styrene-co-acrylonitrile) / Synchrotron Radiation-SAXS / Some investigations 1 -11 have been made on spinodal decompositon (SD) of partially miscible polymer blend systems out of interest in both basic research and industrial applications. Light scattering, electron microscopy etc. have played important roles in these investigations. Studies on the early stage of SD succeeded in verifying the application of the Cahn's theory 12 to polymer blends and also clarification of the mechanism of phase separation.The range of wavelength used in the light scattering experiments is limited so that we are not necessarily able to detect the dominant concentration fluctuation at the early stage SD. X-Rays are sometimes used as a light source to observe segmental order fluctuation. Though small-angle X-ray scattering (SAXS) is favorable from the point of detectable structural dimension, it generally requires long exposure time. So it is not suited for time-resolved measurements of structural change. As far as we know, only a few reports 13 -16 have been published on the application of SAXS for the dynamic study of phase separation of partially miscible blends. In these reports synchrotron radiation (SR) was used as the X-ray source because of its high flux, which is needed to perform time-resolved measurements. Phase separation phenomena were investigated for both upper critical solution temperature (UCST) type blends and lower critical solution temperature (LCST) type blends by time-resolved SR-SAXS: for the UCST type, low molecular weight polystyrene/polybutadiene blends, 13 and for the LCST type, polyt Present address:
We investigated a thermally deposited amorphous silicon (TAS) film before and after annealing. We used monosilane (Sill4) or disilane (Si2H~) as the Si source gas at a deposition pressure of 0.1 to 0.5 Torr. The activation energy of SiH~ deposition was 1.7 eV (560 to 600~ and that of Si2H~ was 0.6 eV (510 to 570~ From TEM observation, the TAS film from 450~ Si2H~ deposition was completely amorphous without crystals and had a smooth surface. Film deposited at 560~ had a few crystals at the Si/SiO2 interface and had a few bumps on the Si surface. After annealing, the mean grain size of 450~ film was about 2 ~m and that of 560~ film was about 0.3 p~m. We also evaluated the crystallinity by XRD and Raman spectroscopy. Films deposited at lower temperatures after annealing showed strong <111>-orientations and high crystal qualities.In ultra large scale integrated (ULSI) device fabrication, vertical size reduction has become as important as reduced overall geometries. Higher quality, thinner films (less than 50 nm) and clean interfaces are needed to fabricate shallower structures. High-quality thin polysilicon films are used as gate electrodes in MOS devices, TFT bodies in SRAMs, emitter electrodes in bipolar devices, capacitor electrodes in DRAMs, and resistors. Also, hemispherical grains (HSG) for capacitor electrodes in 64-MBDRAMs, I'~ and selective polysilicon deposition for filling contacts 3 have been reported. We reported low-temperature Si film deposition from Si2H~ for TFT bodies and electrodes. ~-~ Little research has been done on Si films deposited at temperatures below 550~ because low-temperature deposition is thought to be too slow to be practical. Deposition from higher silanes, however, is expected to produce higher deposition rates at lower temperatures. Before and after annealing, we studied the quality of films deposited from Si2H6 at temperatures ranging from 450 to 620~ We call this film TAS to distinguish it from plasma-enhanced CVD (PECVD) amorphous silicon. ExperimentWe deposited Si films on thermally grown oxide in a low pressure CVD (LPCVD) reactor. We used Sill4 and Si2H~ as Si source gases with the deposition temperatures ranging from 550 to 620~ for Sill4 and 450 to 620~ for Si2H6, and the deposition pressure from 0.2 to 0.5 Torr. For crystallization, we used N2 annealing temperatures ranging from 600-1100~We measured film thicknesses by measuring step heights after Si etching a masked substrate. We evaluated the crystallinity by transmission electron microscopy (TEM), transmission electron diffraction (TED), x-ray diffraction (XRD), and Raman spectroscopy. For TED measurements, we used selected area diffraction. For XRD, we used a special apparatus that allowed measurements of films as thin as 200 nm. We observed surface features with a TEM replica method and scanning electron microscopy (SEM). In the TEM replica method, samples were treated as indicated in Fig. 1. We studied crystallization of samples on a heated stage by micro-Raman spectroscopy. Results and DiscussionDeposition rate.--We...
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