Interface resolved magnetism at metal–organic (Fe/Alq3) interfaces under x-ray standing wave condition

Abstract

The isotope selective grazing-incidence nuclear resonance scattering (GI-NRS) technique, which is a time analog to M€ ossbauer spectroscopy, is made depth resolved to probe the magnetism of the diffused Fe (Fe diffused ) and bulk Fe (Fe bulk ) parts of the layer in an Fe/Alq 3 [ferromagnetic (FM)/organic semiconductor (OSC)] bilayer structure. On the basis of theoretical simulations, it is demonstrated that the antinode regions of x-ray standing waves (XSWs) generated through wave guide structures allow one to measure the Fe diffused and Fe bulk parts independently, providing evidence for a diffused layer with reduced electron density and hyperfine fields. Due to possible small isolated clusters of Fe in the diffused layer, Fe moments are found with random orientations, while in Fe bulk moments, they are aligned in the film plane due to shape anisotropy. GI-NRS under XSW is suitable for FM/OSC structures to obtain interface resolved magnetic information, which is otherwise difficult with any other available lab based conventional methods.

Evolution of the magnetic hyperfine field profiles in an ion-irradiated Fe60Al40 film measured by nuclear resonant reflectivity

“…7(b) are desirable before an experiment, because they help to determine the right choice of angles for NRR spectrum measurements in order to get a real scan of the required properties across the film depth. An example of such an investigation was recently presented by Khanderao et al (2020).…”

“…X-ray reflectometry possesses a sub-nanometre depth resolution for electronic density shaping (Segmü ller, 1973;Liu et al, 2013;Macke et al, 2014) and this technique, complemented with resonant scattering near absorption edges or with nuclear resonant excitation, opens a way for detailed characterization of magnetization depth profiles (see e.g. Ishimatsu et al, 1999;Jaouen et al, 2004;Gibert et al, 2016;Diederich et al, 2007;Schlage et al, 2009;Andreeva et al, 2015Andreeva et al, , 2018Khanderao et al, 2020).…”

Interface magnetism in Fe/Alq3 bilayer; interface resolved nuclear resonance scattering studies

“…Interfaces are crucial in defining and tuning organic devices such as electronic devices based on organic materials such as light-emitting diodes, thin-film transistors, or solar cells. In all such devices, interfaces play a key role in modelling the device properties and their functions [24][25][26][27][28]. The magnetic properties and behavior of metal at the interface is vital in successful working of OSV.…”

“…The high energy ions used in these techniques could result in intermixing and significantly modify the interface. Most of the magnetic measurement techniques provide magnetic information as a whole of the sample, and hence either do not have sufficient depth resolution so as to resolve the interfaces or may not be probing the actual interfaces [25]. X-rays can be made available to probe the interface effectively by confining the X-rays intensity in a specific region along the depth using X-rays standing wave (XSW) generated for waveguide structure [32][33][34].…”

Effect of growth rate on quality of Alq3 films and Co diffusion

“…The ferromagnetic metal penetration effects lead to difficulties in fabricating reliable and reproducible OSVs. A significant amount of research efforts has been carried out for understanding and improving the ferromagnet-OSC interface structure to reduce the diffusion of ferromagnetic material into OSC through interface during sample fabrication [37][38][39][40][41][42]. Thus, the experimental techniques that determine the structural characterization of OSC and depth-resolved structure through interfaces of OSV are most essential.…”