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Grazing-incidence small angle X-ray scattering (GISAXS) analysis of pore size distributions in nano-porous silica films


Nano-porous silica films have potential applications in diverse areas, including biomedical science and nanoelectronics. Evidence has indicated that the pore size and pore size distribution have paramount effects on the properties and/or functionality of the films. Correct and fast evaluation of the average pore size and the pore size distribution is thus an important step in the course of research and development of the nano-porous silica thin film materials.

Small-angle X-ray scattering (SAXS) has long been used for particle/pore size analysis. However, because the silica films are grown on thick substrates, traditional transmission SAXS method can not be applied. To solve this problem, GISAXS, in which the incident angle is controlled to be several tenths of a degree, has to be used. To have the GISAXS measurements done correctly, the sample surface normal has to be aligned correctly and a correct offset angle has to be set to prevent specularly reflected intensities from entering the detector. The SmartLab multipurpose diffractometer, with its proprietary Guidance software, allows this difficult alignment to be completed automatically.


In the figure below, a GISAXS curve of a porous silica film deposited on a silicon substrate measured on the SmartLab is presented, along with the analysis results using Rigaku's Nanosolver software. The simulated curve using a spherical pore/particle model is in excellent agreement with the measurement. From this analysis, it turns out that the film has an average pore size of 5.06 nm and a small size dispersion of just 21.5%.

GISAXS curve of a porous silica film deposited on a silicon substrate