Pawel Nowakowski

Quantification of Grain Boundary Segregation Monolayers by X-ray Spectroscopy in a Scanning Electron Microscope

P. Nowakowski*, F. Christien*, M. Allart*, Y. Borjon-Piron*, R. Le Gall*, J.C. Menard**, H. Mantz*** * Laboratoire Genie des Materiaux et Procedes Associes (LGMPA), Universite de Nantes, Polytech’Nantes, Rue Christian Pauc, BP 50609, 44306 Nantes Cedex 3, France ** Carl Zeiss NTS sas, 27 rue des peupliers, 92752 Nanterre Cedex, France *** Carl Zeiss NTS GmbH, Research & Development, Carl-Zeiss-Strase 56, D-73447 Oberkochen, Germany

RuO2 thin films deposited by spin coating on silicon substrates: pH‐dependence of the microstructure and catalytic properties

RuO2 thin films have been deposited on Si substrates by spin coating with precursor solutions having a pH varying between 1.4 and 4. X‐ray diffraction and transmission electron microscopy analyses are used to determine correlations between the solution pH and the film microstructure. As the pH varies, the RuO2 crystal sizes reach a minimum value then increase; the porosity increases at the substrate/film interface with formation of large cavities. The catalytic activity of these RuO2 layers in the presence of flowing air–methane is analysed by Fourier transform infrared spectroscopy of the conversion of CH4 into CO2. The increasing porosity seems to improve the catalytic conversion rate of methane. Electrical impedance spectroscopy analyses show that the conductivity strongly depends on the thin‐film microstructure and porosity.

The Use of Electron Probe MicroAnalysis to Determine the Thickness of Thin Films in Materials Science

Electron Probe MicroAnalysis (EPMA) was born around 1950 when Raymond Castaing, a French graduate student working under the supervision of Andre Guinier, built his first microanalyser (Castaing & Guinier, 1950; Castaing, 1951; Grillon & Philibert, 2002). The principle of EPMA is to bombard the sample surface with a focused electron beam and to collect the X-rays emitted from the sample. The X-rays are dispersed using Bragg diffraction on a mobile monochromator, which enables to get the whole X-ray spectrum from zero to more than 10 keV. The technique of dispersion is called WDS (Wavelength Dispersive X-ray Spectroscopy). The spectrum is made of continuous background (Bremstrahlung emission) and characteristic peaks, which allow elemental qualitative and quantitative analysis of the material. EPMA-WDS can be carried out in dedicated instruments called “microprobes” (usually fitted with 4 WDS spectometers) or in high current Scanning Electron Microscopes (SEM) equipped with one single WDS spectrometer. More recently, Energy Dispersive X-ray Spectroscopy has been developed and has nowadays become a cheap and widespread technique. Most SEM in materials science laboratories are equipped with an EDS spectrometer. EPMA-EDS performances are far below those of EPMA-WDS with regards to sensitivity and spectral resolution, although it can achieve very good qualitative and quantitative results in many cases. EPMA quantification of the sample composition is usually possible by using a standard material of known composition. Unfortunately there is in general no direct proportionality between the concentration of an element and the X-ray emission intensity (peak height) coming from this element. Since the early years of EPMA, many models have been proposed in the literature to correlate the concentration of an element and the associated X-ray emission intensity: ZAF (Philibert & Tixier, 1968), MSG (Packwood & Brown, 1981), PAP and XPP (Pouchou & Pichoir, 1987; Pouchou et al., 1990)... The XPP model (implemented in several microanalysis software packages) has now reached a good level of maturity and reliability, even in difficult situations involving light elements and strong bulk absorption. It is based on an accurate calculation of the (z) curve, which describes the depth-dependence of the X-ray emission intensity of a particular line in the sample. In EPMA analysis of

Recent Developments in the Study of Grain Boundary Segregation by Wavelength Dispersive X-Ray Spectroscopy (WDS)

It was recently shown [1] that EMPA-WDS (Electron Probe MicroAnalysis by Wavelength Dispersive X-ray Spectroscopy) can be used to detect and to accurately quantify monolayer surface and grain boundary segregation. This paper presents the last developments of this application. It focuses on the measurement of sulphur grain boundary segregation in nickel on fractured surfaces. A special attention was paid to the quantification of the sulphur coverage, taking into account the non-normal incidence of the electron beam on a fracture surface. Sulphur grain boundary segregation kinetics was measured at 750°C in nickel to document the quantitative possibilities of the technique.

Catalytic Studies of RuO2 Films Deposited on Ferroelectrics Films by Spin Coating Process

Films of a catalytic compound (RuO 2 ) were deposited by spin-coating process on ferroelectric films mainly constituted of SrBi 2 Ta 2 O 9 (SBT) and Ba 2 NaNb 5 O 15 (BNN) phases. SBT films were deposited by MOCVD method, and BNN films were deposited by sputtering. After thermal treatment under air, these ferroelectric-catalytic systems were characterized by X-ray diffraction and scanning electron microscopy (SEM). SEM images showed that RuO 2 film morphology depended on substrate nature. A study of CH 4 conversion into CO 2 and H 2 O was carried out using these catalytic-ferroelectric multilayers: the conversion was analyzed from Fourier Transform Infrared (FT-IR) spectroscopy, at various temperatures. Improved catalytic properties were observed for RuO 2 films deposited on BNN oxide layer.