GTSAXS

GTSAXS, or Grazing-incidence Transmission Small-Angle X-ray Scattering is a variant of GISAXS; i.e. it is a surface-sensitive x-ray scattering technique. In GTSAXS, the x-ray beam is directed towards the edge of a sample (rather than the center). This small geometric difference allows the sub-horizon scattering (which is normally attenuated due to substrate absorption) to escape from the sample edge, and be recorded. This sub-horizon scattering is 'cleaner' than conventional GISAXS data. In particular, it suffers much less from the refraction-induced distortion of reciprocal-space and the multiple scattering effects that plague conventional GISAXS.

Geometry of a GTSAXS experiment. In the GTSAXS geometry, the x-ray beam is directed towards the edge of the substrate, so that the direct beam and nearby small-angle scattering can escape without being absorbed by the substrate.

Example of GISAXS data (left) and GTSAXS data (right) for a 'fingerprint' pattern (vertical BCP lamellae). The higher incidence angle of GTSAXS moves the refraction-distortion (and the Yoneda) away from the data. The GTSAXS data is much 'cleaner', as it is not distorted and does not exhibit the 'peak splitting' that arises from multiple-scattering.

Comparison

GTSAXS can be thought of as a combination of a transmission-scattering (TSAXS) and grazing-incidence (GISAXS). In some sense, it combines the simple of data analysis of TSAXS with the surface-sensitive probing of GISAXS.

The main disadvantage of GTSAXS is sample preparation: the material of interest must be near the edge of the substrate. Standard film preparation methods may not yield a representative material near edges. For instance, spin-coating frequently leads to material build-up near substrate edges; this thicker region will dominate the GTSAXS signal, and not be representative of the thin-film structure in the center of the substrate. This can be easily overcome by cleaving substrates, so as to expose a representative edge for probing.

References

• Lu, X.; Yager, K.G.; Johnston, D.; Black, C.T.; Ocko, B.M. Grazing-incidence transmission X-ray scattering: surface scattering in the Born approximation Journal of Applied Crystallography 2013, 46, 165–172. doi: 10.1107/S0021889812047887
• Mahadevapuram, N.; Strzalka, J.; Stein, G.E. Grazing-incidence transmission small angle X-ray scattering from thin films of block copolymers J. Polymer Sci. Part B Polymer Phys. 2013 51, 602610. doi: 10.1002/polb.23261
• Weidman, M.C.; Yager, K.G., Tisdale, W.A. Interparticle Spacing and Structural Ordering in Superlattice PbS Nanocrystal Solids Undergoing Ligand Exchange Chemistry of Materials 2015 doi: 10.1021/cm503626s
• Xinxin Xia, Tsz-Ki Lau, Xuyun Guo, Yuhao Li, Minchao Qin, Kuan Liu, Zeng Chen, Xiaozhi Zhan, Yiqun Xiao, Pok Fung Chan, Heng Liu, Luhang Xu, Guilong Cai, Na Li, Haiming Zhu, Gang Li, Ye Zhu, Tao Zhu, Xiaowei Zhan, Xun-Li Wang & Xinhui Lu Uncovering the out-of-plane nanomorphology of organic photovoltaic bulk heterojunction by GTSAXSNature Communications 2021, 6226 doi: 10.1038/s41467-021-26510-6