We report an investigation of lead halide perovskite CHNHPbBr nanocrystals and associated ligand molecules by combining several different state-of-the-art experimental techniques, including synchrotron radiation-based XPS and VUV PES of free-standing nanocrystals isolated in vacuum. By using this novel approach for perovskite materials, we could directly obtain complete band alignment to vacuum of both CHNHPbBr nanocrystals and the ligands widely used in their preparation. We discuss the possible influence of the ligand molecules to apparent perovskite properties, and we compare the electronic properties of nanocrystals to those of bulk material. The experimental results were supported by DFT calculations.
We
report on the aerosol generation of ligand-free silver iodobismuthate
(Ag-Bi-I) nanoparticles (NPs) and on in situ investigation of their
electronic structure using synchrotron radiation soft X-ray aerosol
photoelectron spectroscopy (XAPS). The structural and morphological
characterizations revealed the aerosol to be composed of spherical
rudorffite Ag3BiI6 particles, approximately
100 nm in size. The XAPS showed well-resolved signals from all expected
elements (Ag, Bi, and I) and allowed estimation of the NP work function
to be about 4.5 eV. The ionization energy of Ag3BiI6 NPs was determined to be 6.1 eV that is in good agreement
with our calculations based on a hybrid functional approach. The presented
method of production of Ag3BiI6 aerosol can
prove beneficial for the future development of Ag-Bi-I-based photovoltaic
materials, since it allows the deposition of Ag-Bi-I particles on
large surface areas of arbitrary shape and roughness.
The influence of the mechanical activation of ZnO nanoparticle fillers on the structural and electrical properties of the matrix of poly(vinylidenefluoride)-ZnO (PVDF-ZnO) films was investigated. Transmission electron microscopy and scanning electron microscopy analyses showed that mechanical activation in a high energy planetary ball mill reduces the size of ZnO particles. X-ray diffraction and Raman spectroscopy revealed that PVDF crystallized predominantly as the -phase. Non-activated ZnO filler reduces the degree of the crystallinity of the matrix and promotes crystallization of α-phase of PVDF in the film, while the fillers activated for 5 and 10 min induce crystallization of -phase, indicating that mechanical activation of the filler can be used as a general method for fabrication of PVDF composites with increased content of piezoelectric -phase crystals.Dielectric spectroscopy measurements show that polymer composite with the high content of -phase (with ZnO filler activated for 5 min) exhibits the highest value of dielectric permittivity in 150-400 K range of temperatures. Kinetic analysis shows combined effects of increased surface area and increased concentration of surface defects on the interactions between polymer chains and activated nanoparticles.
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