Characterization of multilayer stack parameters from x-ray reflectivity data using the PPM program: measurements and comparison with TEM results

Abstract

Future hard (10 -100 keV) X-ray telescopes (SIMBOL-X, Con-X, HEXIT-SAT, XEUS) will implement focusing optics with multilayer coatings: in view of the production of these optics we are exploring several deposition techniques for the reflective coatings. In order to evaluate the achievable optical performance X-Ray Reflectivity (XRR) measurements are performed, which are powerful tools for the in-depth characterization of multilayer properties (roughness, thickness and density distribution). An exact extraction of the stack parameters is however difficult because the XRR scans depend on them in a complex way. The PPM code, developed at ERSF in the past years, is able to derive the layer-by-layer properties of multilayer structures from semi-automatic XRR scan fittings by means of a global minimization procedure in the parameters space. In this work we will present the PPM modeling of some multilayer stacks (Pt/C and Ni/C) deposited by simple e-beam evaporation. Moreover, in order to verify the predictions of PPM, the obtained results are compared with TEM profiles taken on the same set of samples. As we will show, PPM results are in good agreement with the TEM findings. In addition, we show that the accurate fitting returns a physically correct evaluation of the variation of layers thickness through the stack, whereas the thickness trend derived from TEM profiles can be altered by the superposition of roughness profiles in the sample image.

Silicon oxide-niobium oxide mixture films and nanolaminates grown by atomic layer deposition from niobium pentaethoxide and hexakis(ethylamino) disilane

“…The period of the superlattice maxima becomes gradually longer or shorter as the bilayer thickness decreases or increases, respectively [54][55][56][57]. The shorter oscillation period is inversely proportional to the total nanolaminate thickness.…”

“…3). The highest sharp maxima that are the most prominent, are characteristic of the superlattice structures [54][55][56][57] and indicate that the bilayers are uniform with appreciably sharp interfaces.…”

Analysis of microroughness evolution in X-ray astronomical multilayer mirrors by surface topography with the MPES program and by X-ray scattering

“…(10) λ (= 1.541 Å) is known, ϑ i , ϑ s , I 0 , I s , can be are measured directly, R is is computed from Fresnel equations, the T j coefficients can be derived from the multilayer reflectivity, computed using a standard method 20,24 . In this work the incidence we simplify the T j coefficients by taking XRS detector scans with incidence angle at the k th Bragg peak: therefore, the electric field falls exponentially 24 in the stack.…”

“…Along with Xray reflectivity tests at 8.05 keV (Cu-Kα line) performed with a Bede-D1 diffractometer we have inferred the multilayers structure. In order to interpret these data we have used the IMD 18 program and, for multilayers exhibiting evidence of dspacing drift along the stack, the PPM 19 program (see also this conference 20 ). All multilayers have a periodic or quasiperiodic structure.…”

Optical and structural characterization of CeO2/B4C multilayers near boron K-edge energy

“…The presence of interdiffusion can be clearly observed which causes superposition of CeO2 and B4C atoms around the interfaces. This superposition might cause thickness profiles in the SEM image affected by a significant error [30]. A close look up into the onset in Fig 10 proves that the ambiguity to determine optical boundaries where real reflection takes place from the SEM image.…”