The energy dispersive x-ray reflectometry as a unique laboratory tool for investigating morphological properties of layered systems and devices

Abstract

The principles and technical aspects of the laboratory energy dispersive x-ray reflectometry technique (EDXR) are reviewed. X-ray reflectometry enables us to retrieve information on the morphological parameters (film thickness, surface and interface roughness) of thin films, layered materials and devices at the Å resolution. In the energy dispersive mode it makes use of a polychromatic beam and the energy scan is carried out by means of an energy sensitive detector, allowing us to keep the experimental geometry unchanged during data collection. The advantages offered by the technique, in particular when accurate time-resolved studies are to be performed, are outlined. An overview of the most significant works in the field is also reported, in order to present the wide range of its possible applications. The paper was written taking into account the necessity to provide a comprehensive description of this unusual laboratory technique. The first part of the manuscript is, therefore, devoted to the general aspects of EDXR: theoretical bases, experimental characteristics, advantages and drawbacks in comparison with alternative techniques, instrumental effects that may occur and information that can be gained by its application. In the second part of the paper, we resume the main literature results obtained by applying it to a variety of systems, to show examples of the possibilities it offers. Among the experiments reported, in particular much emphasis is given to the time-resolved in situ ones (for example, devices upon working and systems undergoing morphological modifications), which probably represents the most original use of this method.

Structural/morphological monitoring approach to stability and durability issues of photoactive films for organic solar cells

“…The joint X-ray/AFM measurements were performed using a non-commercial X-ray machine [17,18] integrated with a homemade atomic force microscope [20]. The Bremmsstrahlung of the X-ray tube (3 kW power, tungsten anode) was used as a probe and a EG&G high purity germanium solid-state detector, whose energy resolution is about 1.5-2% in the 20-50 keV energy range, accomplished the energy scan.…”

“…Time-resolved Energy Dispersive X-ray Diffraction (EDXD) was applied, in synergy with Atomic Force Microscopy (AFM) experiments, to perform 'non-perturbative and nondestructive' investigations. In the ED mode [17,18], the patterns are collected using a polychromatic beam and carrying out an energy scan of the diffracted radiation by means of an energy sensitive detector. Indeed, the diffracted intensity is a function of the momentum transferred from the X-rays to the sample electrons.…”

Exchange Bias in fcc-CoPt/CoO/Si films as a function of annealing treatment

“…In this unconventional mode, the reciprocal space scan (q-scan, where q is the normalized momentum transfer magnitude), necessary to collect the diffraction pattern, is carried out electronically, rather than mechanically, as in the conventional X-ray diffraction [7]. Moreover, ED X-ray Reflectometry [8] measurements were performed to obtain information on the film thickness and roughness, this technique being sensitive to surface and interface morphology at the angstrom resolution [9].…”

Gas sensing (RuPc)2 thin films: Electrical response to NO2 gas and morphological changes induced by external moisture

“…A reflectivity measurement consists of collecting the reflected intensity as a function of the scattering parameter, q = 4 sin˛/ = KE sin˛(K = 1.014 is a constant value, E the radiation energy and˛is half the scattering angle), which depends on the radiation energy and the scattering angle. It follows that two methods are available for carrying out the q scan and reflected intensity profile as a function of q [17]. The first is to use a monochromatic beam (fixed energy), for instance a fluorescence line produced by a laboratory X-ray tube, and to make an angular scan, called angular dispersive (AD) mode.…”