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Sci Rep ; 9(1): 5811, 2019 Apr 09.
Artigo em Inglês | MEDLINE | ID: mdl-30967593


The valid strong THz absorption at 1.58 THz was probed in the organic-inorganic hybrid perovskite thin film, CH3NH3PbI3, fabricated by sequential vacuum evaporation method. In usual solution-based methods such as 2-step solution and antisolvent, we observed the relatively weak two main absorption peaks at 0.95 and 1.87 THz. The measured absorption spectrum is analyzed by density-functional theory calculations. The modes at 0.95 and 1.87 THz are assigned to the Pb-I vibrations of the inorganic components in the tetragonal phase. By contrast, the origin of the 1.58 THz absorption is due to the structural deformation of Pb-I bonding at the grain boundary incorporated with a CH3NH2 molecular defect.

J Phys Chem Lett ; 9(9): 2293-2297, 2018 May 03.
Artigo em Inglês | MEDLINE | ID: mdl-29667412


To understand the instability of Sn-based perovskite, CH3NH3SnI3, photoelectron spectroscopy with synchrotron radiation and theoretical calculations, such as density functional theory and ab initio molecular dynamics, were performed. Findings from this experimental and theoretical study highlight the crucial changes of surface-chemical states, the broken chemical bondings in Sn-I, and the depletion of a CH3-NH3+ cation on the surface region. The material instability origin of Sn-based perovskite can be explained by the chemical state instability in the surface.

Phys Chem Chem Phys ; 14(48): 16552-7, 2012 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-22772941


As a first step towards a microscopic understanding of single-Pt atom-dispersed catalysts on non-conventional TiN supports, we present density-functional theory (DFT) calculations to investigate the adsorption properties of Pt atoms on the pristine TiN(100) surface, as well as the dominant influence of surface defects on the thermodynamic stability of platinized TiN. Optimized atomic geometries, energetics, and analysis of the electronic structure of the Pt/TiN system are reported for various surface coverages of Pt. We find that atomic Pt does not bind preferably to the clean TiN surface, but under typical PEM fuel cell operating conditions, i.e. strongly oxidizing conditions, TiN surface vacancies play a crucial role in anchoring the Pt atom for its catalytic function. Whilst considering the energetic stability of the Pt/TiN structures under varying N conditions, embedding Pt at the surface N-vacancy site is found to be the most favorable under N-lean conditions. Thus, the system of embedding Pt at the surface N-vacancy sites on TiN(100) surfaces could be promising catalysts for PEM fuel cells.