Topographic measurement of buried thin-film interfaces using a grazing resonant soft x-ray scattering technique

Abstract

The internal structures of thin films, particularly interfaces between different materials, are critical to system properties and performance across many disciplines, but characterization of buried interface topography is often unfeasible. In this work, we demonstrate that Grazing Resonant Soft X-ray Scattering (GRSoXS), a technique using diffusely scattered soft X-rays in grazing incidence geometry, can reveal the statistical topography of buried thin film interfaces. By controlling and predicting the X-ray electric field intensity throughout the depth of the film and simultaneously the scattering contrast between materials, we are able to unambiguously identify the microstructure at different interfaces of a model polymer bilayer system. We additionally demonstrate the use of GRSoXS to selectively measure the topography of the surface and buried polymer-polymer interface in an organic thin film transistor, revealing different microstructure and markedly differing evolution upon annealing. In such systems, where only indirect control of interface topography is possible, accurate measurement of the structure of interfaces for feedback is critically important. While we demonstrate the method here using organic materials, we also show that the technique is readily extendable to any thin film system with elemental or chemical contrasts exploitable at absorption edges.

Quantitative Morphology–Performance Correlations in Organic Solar Cells: Insights from Soft X‐Ray Scattering

“…R-SoXS affords a quantitative determination of the dominant domain spacing (long period), domain distribution (structures at multiple length-scales), and relative average composition variation and P-SoXS quantifies the degree of molecular orientation relative to the D/A interface within the bulk-heterojunction of photoactive layers of OPVs. It is noteworthy that novel grazing incident soft X-ray scattering (GI-RSoXS) [152] is also powerful to understand the complex morphology of ternary blend OPVs. [57] Based on the quantitative parameters gained from these synchrotron-based soft X-ray scattering and related techniques, both novel material synthesis and device optimization studies during the last several years have benefited greatly from dedicated and detailed morphological characterizations of the devices.…”

Spectral Analysis for Resonant Soft X-Ray Scattering Enables Measurement of Interfacial Width in 3D Organic Nanostructures

“…However, complex scattering models beyond the Born Approximation 39,40 are required to quantitatively interpret such data. Instead we retain the simplicity of transmission geometry by rotating the film from normal incidence to 20° as shown in Figure 3a.…”

Micro-imaging of buried layers and interfaces in ultrathin films by X-ray reflectivity

“…By controlling the grazing incidence, one can manipulate the penetration depth of X-rays into a thin film and change electric field in-depth distribution in the sample. 17 X-ray reflectivity is a measurement scanning grazing incidence and probing the structure of thin films in depth. By choosing specific grazing incidence (thus wavevector transfer Q z ), one can obtain a proper electric field and then emphasize specific layers or interfaces in the sample.…”