1 research outputs found
New Approach on Quantification of Porosity of Thin Films via Electron-Excited X‑ray Spectra
One
of the crucial characteristics of functionalized thin films
is their porosity (i.e., the ratio between the pore volume and the
volume of the whole film). Due to the very low amount of material
per coated area corresponding to thin films, it is a challenge for
analytics to measure the film porosity. In this work, we present an
approach to determine the porosity of thin films by means of electron
probe microanalysis (EPMA) either by wavelength-dispersive X-ray spectrometry
(WDX) or by energy-dispersive X-ray spectrometry (EDX) with a scanning
electron microscope (SEM). The procedure is based on the calculation
of the film mass deposition from electron-excited X-ray spectra. The
mass deposition is converted into film density by division of measured
film thickness. Finally, the film porosity is calculated from the
measured film density and the density of bulk, nonporous film material.
The general applicability of the procedure to determine the porosity
is demonstrated on thin templated mesoporous TiO<sub>2</sub> films,
dip-coated on silicon wafer, with controlled porosity in the range
of 15 to 50%. The high accuracy of the mass deposition as determined
from X-ray spectra was validated with independent methods (ICP-OES
and weighing). Furthermore, for the validation of the porosity results,
ellipsometry, interference fringes method (IFM), and focused ion beam
(FIB) cross sectioning were employed as independent techniques. Hence,
the approach proposed in the present study is proven to be suited
as a new analytical tool for accurate and relatively fast determination
of the porosity of thin films