Site-selective spectroscopy with depth resolution using resonant x-ray reflectometry

Abstract

Combining dissimilar transition metal oxides (TMOs) into artificial heterostructures enables to create electronic interface systems with new electronic properties that do not exist in bulk. A detailed understanding of how such interfaces can be used to tailor physical properties requires characterization techniques capable to yield interface sensitive spectroscopic information with monolayer resolution. In this regard resonant x-ray reflectivity (RXR) provides a unique experimental tool to achieve exactly this. It yields the element specific electronic depth profiles in a non-destructive manner. Here, using a YBa2Cu3O7−δ (YBCO) thin film, we demonstrate that RXR is further capable to deliver site selectivity. By applying a new analysis scheme to RXR, which takes the atomic structure of the material into account, together with information of the local charge anisotropy of the resonant ions, we obtained spectroscopic information from the different Cu sites (e.g., chain and plane) throughout the film profile. While most of the film behaves bulk-like, we observe that the Cu-chains at the surface show characteristics of electron doping, whereas the Cu-planes closest to the surface exhibit an orbital reconstruction similar to that observed at La1−xCaxMnO3/YBCO interfaces.

Simultaneous Observation of Carrier-Specific Redistribution and Coherent Lattice Dynamics in 2H-MoTe2 with Femtosecond Core-Level Spectroscopy

“…22,26 The element-specificity inherent to core-level spectroscopy offers the additional capability to distinguish the individual subcomponent materials in heterostructures. 27,28 Finally, the unique sensitivity of core-level spectroscopy to bonding, bond distances, and symmetry provides simultaneous structural information of photoexcited materials. [29][30][31][32][33][34] In the present study, we apply sub-5 fs XUV transient absorption spectroscopy on a 2H-MoTe2 semiconductor thin film (~50 nm/70 layers) to probe the dynamics of intraband carrierspecific relaxation, interband electron-hole recombination, and excited-state coherent lattice displacement.…”

“…In some cases, photoexcited holes and electrons can be separately and simultaneously attributed to changes in spectrally distinct transitions from atomic core levels to the transiently empty states in the VB (holes) and reduced absorption in the transiently filled CB (electrons). These phenomena are collectively referred to here as “state-filling.” It is possible not only to distinguish the hole and electron distributions but also to gain energy-dependent dynamics of the specific hot carriers within the VB and CB. , The element-specificity inherent to core-level spectroscopy offers the additional capability to distinguish the individual subcomponent materials in heterostructures. , Finally, the sensitivity of core-level spectroscopy to bonding, bond distances, and symmetry provides simultaneous structural information on photoexcited materials. − …”

Transition from a uni- to a bimodal interfacial charge distribution in $$\hbox {LaAlO}_3$$/$$\hbox {SrTiO}_3$$ upon cooling

“…Their thickness and stacking has been defined according to precise crystallographic data for LAO/STO heterostructures 21 , 22 . For each of the atomic slices an energy dependent index of refraction was then calculated using the of the elements and their concentrations 20 , 23 , 24 . Regarding the termination of substrate and film, the LAO/STO interface in the models was fixed to be TiO -LaO, since the films were grown on TiO -terminated substrates, whereas no preference for the surface termination of LAO was assumed.…”

Complementary Insights from Neutron and Resonant X‐Ray Reflectometry for the Study of Perovskite Transition Metal Oxide Heterostructures

“…[24] As such, XR(M)R allows one to determine the depthresolved, element-specific electronic and magnetic properties in a complex oxide heterostructure. Particularly noteworthy XR(M) R studies have been carried out on synchrotrons such as HZB-BESSY II, [25][26][27] SOLEIL, [28] CLS, [29] SLS, [30] ALS, [31] APS, [32] and ALBA, [33] where specialized setups are available.…”