X-RAY-DIFFRACTION AND X-RAY-ABSORPTION STUDIES OF POROUS SILICON, SILOXENE, HEAT-TREATED SILOXENE, AND LAYERED POLYSILANE

Several porous silicon, siloxene (Si6H6O3), heat-treated siloxene, and layered polysilane (Si6H6) samples have been studied with K- and L-ed ge x-ray photoabsorption, photoemission, and powder x-ray diffraction. The x-ray absorption of layered polysilane and porous-Si are found to be remarkably similar. In particular, the K absorption edges of these samples shift by about 0.4-0.6 eV to higher energy relative to crysta lline silicon. Siloxene samples heated to 400-degrees-C in inert gas a re best described as a mixture of SiO2 and amorphous-Si. When heat-tre ated siloxene is studied by photoelectron spectroscopy (surface sensit ive) it resembles SiO2, when it is studied by x-ray absorption (bulk a nd surface) features from both SiO2 and amorphous-Si are observed and when it is studied by x-ray diffraction (bulk measurement) it resemble s amorphous-Si. The SiO2 is therefore predominantly at the surface and heat-treated siloxene is very small amorphous-Si particles coated wit h SiO2. The Si L edge of heat-treated siloxene is not shifted signific antly with respect to crystalline Si, unlike that of porous-Si, as-pre pared siloxene, or layered polysilane. Taken together, these results s uggest that heat-treated siloxene does not resemble electrochemically prepared porous-Si but that it might resemble rapid thermal annealed p orous-Si. On the other hand, we believe that layered polysilane and un heated porous-Si may be related.