title: New Approach on Quantification of Porosity of Thin Films via Electron-Excited X-ray Spectra.
abstract: 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 TiO2 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.
authors.affiliation: Federal Institute for Materials Research and Testing (BAM), Berlin 12200, Germany.
authors.forename: Erik
authors.initials: E
authors.lastname: Ortel
authors.affiliation: Federal Institute for Materials Research and Testing (BAM), Berlin 12200, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hertwig
authors.affiliation: Technische Universität Berlin, Straße des 17. Juni 135, Berlin 10623, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Berger
authors.affiliation: Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, Turin 10135, Italy.
authors.forename: Pasquale
authors.initials: P
authors.lastname: Esposito
authors.affiliation: Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, Turin 10135, Italy.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Rossi
authors.affiliation: Technische Universität Berlin, Straße des 17. Juni 135, Berlin 10623, Germany.
authors.forename: Ralph
authors.initials: R
authors.lastname: Kraehnert
authors.affiliation: Federal Institute for Materials Research and Testing (BAM), Berlin 12200, Germany.
authors.forename: Vasile-Dan
authors.initials: VD
authors.lastname: Hodoroaba