Spectroscopic characterization of electronic structures of ultrathin freestanding single crystal films

Chun-Chien Chiu^1*, Yao-Wen Chang¹, Yu-Chang Shao², Yu-Chen Liu¹, Jenn-Min Lee³, Shih- Wen Huang³, Wanli Yang², Jinghua Guo², Frank M. F. de Groot⁴, Jan-Chi Yang¹, Yi-De Chuang²

¹Department of Physics, National Cheng Kung University, Tainan, Taiwan
²Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA, USA
³MAX IV Laboratory, Lund University, P. O. Box 118, 221 00 Lund, Sweden
⁴Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, Netherlands

* Presenter:Chun-Chien Chiu, email:l28091025@gs.ncku.edu.tw

The measurement of the true soft X-ray absorption typically needs specially prepared ultrathin samples for transmission measurements. The current bulk measurement must rely on indirect methods, such as total electron yield and fluorescence yield. These methods some exhibit challenging limitation and deficiency. In this work, a high quality single crystalline La_0.7Sr_0.3MnO₃ (LSMO) ultrathin film have been fabricated successfully. The ultrathin LSMO films are transferred onto silicon wafer and copper mesh via oxide freestanding technique. We demonstrate that the x-ray emission from Mn 3s-2p core-to-core transition (3sPFY) seen in the RIXS maps can represent the bulk-like absorption signal with minimal self-absorption effect around the Mn L₃-edge via soft x-ray absorption (XAS) and resonant inelastic x-ray scattering (RIXS) spectroscopy in transmission and reflection geometries. Similar measurements were also performed on a reference LSMO film grown on the SrTiO₃ substrate and the agreement between measurements substantiates the claim that the bulk electronic structures can be preserved even after the freestanding transfer process. Our results provide a powerful approach to probe the bulk electronic structures of thin films and heterostructures using XAS spectroscopy in transmission mode.

Keywords: Freestanding, 3s-2p core-to-core transition, true soft X-ray absorption, resonant inelastic x-ray scattering (RIXS)