Large-grain polycrystalline silicon films with low intragranular defect density by low-temperature solid-phase crystallization without underlying oxide
The solid-phase crystallization of an amorphous silicon film to polycrystalline silicon by a low-temperature (⩽600 °C) furnace anneal has been investigated in a suspended cantilever structure without underlying silicon oxide by transmission electron microscopy and Raman spectroscopy. The grain size of polysilicon increases up to ∼3.0 μm and the density of intragranular defects decreases one order of magnitude in the samples without underlying oxide, compared with those with underlying oxide. The main reasons for the high quality of the suspended structures are thought to be due to the lower stress in the films during crystallization and a reduced grain nucleation rate.
Raman, transmission electron microscopy, and conductivity measurements in molecular beam deposited microcrystalline Si and Ge: A comparative study
The structure of molecular beam deposited microcrystalline silicon and germanium films prepared under different growth conditions has been analyzed by conventional transmission electron microscope (TEM) and Raman scattering (RS) and compared to electrical conductivity experiments. The TEM measurements yield an average grain size L0 ranging from 200 A to 1.5 μm. On the other hand, the line shape of the RS is determined by a mean free path related to the average separation l between defects (or impurities), where l≤150 A. We find in a number of cases that the electrical conductivity is determined by l rather than L0. This experiment demonstrates the significance of RS as a structural characterization method when used in conjunction with other techniques such as TEM.
Preparation of hydrophilic poly(vinyl butyral) hollow fiber membrane via thermally induced phase separation
Abstract Hydrophilic microporous hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Poly(vinyl butyral) (PVB) and three kinds of polyethylene glycols (PEG) with the molecular weight of 200, 400 and 600 were used as polymer and diluents. In all cases, liquid–liquid (L–L) phase separation occurred and asymmetric cellular structures with the smaller pores at the outer surface were obtained. The properties of membranes such as pore size, water permeability, solute rejection and intensity were investigated by changing molecular weight of PEG, concentration of PVB, composition of the bath and air gap distance. The smaller molecular weight of PEG, the more PEG in the bath and the shorter air gap distance resulted in the higher water permeability, the lower solute rejection property and the lower mechanical strength.