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CuInP2S6 (CIPS) is an emerging 2D ferroelectric material known for disrupting spatial inversion symmetry due to Cu(I) position switching. Its ferroelectricity strongly relies on the Cu(I) atom/ion occupation ordering and dynamics. Nevertheless, the accurate Cu(I) occupations and correlated migration dynamics under the externally applied energy, which are key to unlocking ferroelectric properties, remain controversial and unresolved. Herein, an atomic-level direct imaging through aberration-corrected scanning transmission electron microscopy is performed to precisely trace the Cu(I) dynamic behaviours under electron-beam irradiation along (100)-CIPS. It clearly demonstrates that Cu(I) possesses multiple occupations, and Cu(I) could migrate to the lattice, vacancy, interstitial and interlayer sites between the InS6 octahedral skeletons of CIPS to form local CuxInP2S6 (x = 2-4) structure. Cu(I) multi-occupations induced lattice stress results in a layer sliding along the b-axis direction generating a sliding size of 1/6 b lattice constant. The CuxInP2S6 (x = 2-4) exists in a type of dynamic structure, only metastable with electron dose over 50 e− Å−2, thus generating a dynamic process of C u x In P 2 S 6 (x = 2 − 4) ⇌ CuIn P 2 S 6 , a completely unreported phenomenon. These findings shed light on the unveiled mechanism underlying Cu(I) migration in CIPS, providing crucial insights into the fundamental processes that govern its ferroelectric properties. The authors demonstrate that Cu(I) possesses multiple occupations, and Cu(I) migrate to the lattice, vacancy, interstitial and interlayer sites between the InS6 octahedral skeletons of CuInP2S6 to form local CuxInP2S6 (x = 2-4) structure. [ABSTRACT FROM AUTHOR]

Organic anode materials have attracted considerable interest owing to their high tunability by adopting various active functional groups. However, the interaction mechanisms between the alkali metals and the active functional groups in host materials have been rarely studied systematically. Here, a widely used organic semiconductor of perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) was selected as a model system to investigate how alkali metals interact with imide functional groups and induce changes in chemical and electronic structures of PTCDI. The interaction at the alkali/PTCDI interface was probed by in-situ X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), synchrotron-based near edge X-ray absorption fine structure (NEXAFS), and corroborated by density functional theory (DFT) calculations. Our results indicate that the alkali metal replaces the hydrogen atoms in the imide group and interact with the imide nitrogen of PTCDI. Electron transfer induced gap states and downward band-bending like effects are identified on the alkali-deposited PTCDI surface. It was found that Na shows a stronger electron transfer effect than Li. Such a model study of alkali insertion/intercalation in PTCDI gives insights for the exploration of the potential host materials for alkali storage applications. [ABSTRACT FROM AUTHOR]

Nitrogen fixation is a vital process for both nature and industry. Whereas the nitrogenase can reduce nitrogen in ambient environment in nature, the industrialized Haber-Bosch process is a high temperature and high-pressure process. Since the discovery of the first dinitrogen complex in 1965, many dinitrogen complexes are prepared in a homogeneous solution to mimic the nitrogenase enzyme in nature. However, studies of the heterogeneous process on surface are rarely addressed. Moreover, molecular scale characterization for such dinitrogen complex is lacking. Here, we present a simple model system to investigate, at the single-molecule level, the binding of dinitrogen on a surface confined iron phthalocyanine (FePc) monolayer through the combination of in-situ low-temperature scanning tunneling microscopy (LT-STM) and X-ray photoelectron spectroscopy (XPS) measurements. The iron center in FePc molecule deposited on Au(111) and highly oriented pyrolytic graphite (HOPG) surface can adsorb dinitrogen molecule at room temperature and low pressure. A comparative study reveals that the adsorption behaviors of FePc on these two different substrates are identical. Chemical bond is formed between the dinitrogen and the Fe atom in the FePc molecule, which greatly modifies the electronic structure of FePc. The bonding is reversible and can be manipulated by applying bias using a STM tip or by thermal annealing. [ABSTRACT FROM AUTHOR]