Towards silver fluoride quantum materials

Motivated by the analogy of Ag2+ fluorides with high-Tc cuprate superconductors, this work investigates the synthesis and characterization of silver fluorides. A custom ultra-high vacuum (UHV) chamber was developed for the fluorination of surfaces. We discovered a protocol that allows the production of monatomic fluorine in an ultra-clean environment. We used the chamber to study the interaction of Ag(100) and Ag(110) surfaces with atomic fluorine using scanning tunneling microscopy (STM) supported by density functional theory (DFT) calculations. The preferred fluorine adsorption sites were identified. We estimated an anomalously low initial sticking coefficient of monatomic fluorine for the Ag(100) (S0 ≈ 10(−5)) and the Ag(110) surfaces (S0 ≈ 10(−4)). At higher fluorine coverages, we found that the sticking coefficient grows by more than an order of magnitude. Furthermore, the system phase separates into fluorine-poor and fluorine-rich disordered regions. This phenomenon was modeled using a two-dimensional Van der Waals theory. The Ag(100) surface has a stronger tendency to phase separation compared to the Ag(110) surface, which could be related to an attractive fluorine-fluorine interaction potential deduced from the low-coverage correlation functions. These results pave the way to the synthesis and engineering of two-dimensional silver fluoride quantum materials. Furthermore, to characterize bulk silver fluoride phases, powder samples of the two-dimensional antiferromagnet (AF) AgF2 and the one-dimensional AF AgFBF4 were examined using X-ray absorption spectroscopy and resonant inelastic X-ray scattering. We found that spectral features—such as dd and charge-transfer excitations—closely resemble those of La2CuO4. These findings highlight AgF2 as a promising platform to mimic the physics of cuprates without copper and to investigate correlated electron physics and unconventional superconductivity in silver fluorides. With this perspective, we collaborated with a company in the design of a custom-made chamber for pulsed laser deposition of silver fluorides.