Browsing by Author "Sapkota, Pitambar"

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    Aerosol Synthesis and Gas-Phase Photoelectron Spectroscopy of Ag-Bi-I Nanosystems
    Danilović, Danijela; Božanić, Dušan; Dojčilović, Radovan; Vukmirović, Nenad; Sapkota, Pitambar; Vukašinović, Ivana; Đoković, Vladimir; Bozek, John; Nicolas, Christophe; Ptasinska, Sylwia; Milosavljević, Aleksandar
    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.
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    Electronic Properties of Free-Standing Surfactant-Capped Lead Halide Perovskite Nanocrystals Isolated in Vacuo
    Milosavljević, Aleksandar R.; Božanić, Dušan K.; Sadhu, Subha; Vukmirović, Nenad; Dojčilović, Radovan; Sapkota, Pitambar; Huang, Weixin; Bozek, John; Nicolas, Christophe; Nahon, Laurent; Ptasinska, Sylwia
    We report an investigation of lead halide perovskite CH3NH3PbBr3 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 CH3NH3PbBr3 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.
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    Electronic Properties of Silver–Bismuth Iodide Rudorffite Nanoplatelets
    Danilović, Danijela; Milosavljević, Aleksandar R.; Sapkota, Pitambar; Dojčilović, Radovan; Tošić, Dragana; Vukmirović, Nenad; Jocić, Milan; Djoković, Vladimir; Ptasinska, Sylwia; Božanić, Dušan K.
    Silver-bismuth iodide (Ag-Bi-I) rudorffites are chemically stable and non-toxic materials that can act as a possible lead-free replacement for methylammonium lead halides in optoelectronic applications. We report on a simple route for fabricating Ag-Bi-I colloidal nanoplatelets approximately 160 nm in lateral dimensions and 1-8 nm in thickness via exfoliation of Ag-Bi-I rudorffite powders in acetonitrile. The valence band electronic structure of isolated Ag-Bi-I nanoplatelets was investigated using synchrotron radiation to perform X-ray aerosol photoelectron spectroscopy (XAPS). The ionization energy of the material was found to be 6.1 +/- 0.2 eV with respect to the vacuum level. UV-vis absorption and photoluminescence spectroscopies of the Ag-Bi-I colloids showed that the optical properties of the nanoplatelets originate from I 5p to Bi 6p and I 5p to I 5p transitions, which is further confirmed by density functional theory (DFT) calculations. Finally, calculations based on the DFT and k . p theoretical methods showed that the quantum confinement effect is very weak in the system studied.