Nanoscale mapping of chemical composition in organic-inorganic hybrid perovskite films

Lead-based organic-inorganic hybrid perovskite (OIHP) solar cells can attain efficiencies over 20%. However, the impact of ion mobility and/or organic depletion, structural changes, and segregation under operating conditions urge for decisive and more accurate investigations. Hence, the development of analytical tools for accessing the grain-to-grain OIHP chemistry is of great relevance. Here, we used synchrotron infrared nanospectroscopy (nano-FTIR) to map individual nanograins in OIHP films. Our results reveal a spatial heterogeneity of the vibrational activity associated to the nanoscale chemical diversity of isolated grains. It was possible to map the chemistry of individual grains in CsFAMA [Cs_0.05FA_0.79MA_0.16Pb(I_0.83Br_0.17)₃] and FAMA [FA_0.83MA_0.17Pb(I_0.83Br_0.17)₃] films, with information on their local composition. Nanograins with stronger nano-FTIR activity in CsFAMA and FAMA films can be assigned to PbI₂ and hexagonal polytype phases, respectively. The analysis herein can be extended to any OIHP films where organic cation depletion/accumulation can be used as a chemical label to study composition.

New model for magnetism in ultrathin fcc Fe on Cu(001)

Using soft-x-ray resonant magnetic scattering in combination with first-principles calculations for noncollinear magnetic configurations we present a new model of the magnetism in ultrathin fcc Fe films on Cu(001). We find the presence of blocks with robust magnetic structure, while the relative directions of the moments of different blocks are sensitive to the detailed atomic structure and temperature. The magnetic noncollinearity is directly demonstrated, which has not been possible so far.

Depth magnetization profile of a perpendicular exchange coupled system by soft-x-ray resonant magnetic reflectivity

The magnetic profile across the interface of a perpendicular exchange coupled [NiO/CoO]3/Pt-Co/Pt(111) system is investigated. The magneto-optic Kerr effect reveals a strong coupling between the antiferromagnetic (AFM) oxide and the ferromagnetic (FM) Pt-Co layer, by an increasing coercivity and a rotation of the easy magnetization axis of the FM layer along the AFM spins. Soft x-ray resonant magnetic reflectivity is used to probe the spatial distribution of the out-of-plane magnetization inside the oxide above its ordering temperature. It extends over 1 nm and exhibits a change of sign.

Controlling structure and morphology of CoPt nanoparticles through dynamical or static coalescence effects

The structure and morphology of 1 to 3 nm size CoPt nanoparticles have been investigated in situ and in real time under different conditions: growth at 500 degrees C or at room temperature (RT) followed by annealing at 500 degrees C. The small-angle x-ray scattering measurements show size and temperature dependent growth mode with particle motions on the surface, while wide-angle scattering results, supported by Monte Carlo simulations, allow structure identification. If icosahedra are systematically detected at the first growth stages at RT, annealing at 500 degrees C yields the decahedral structure from the quasistatic coalescence of icosahedral morphology. Meanwhile, growth at 500 degrees C proceeds by a dynamical coalescence mechanism at the early stage, yielding truncated octahedral cubic structures.