A series of two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) crystals, based on acene alkylamine cations (i.e., phenylmethylammonium (PMA), 2-phenylethylammonium (PEA), 1-(2-naphthyl)methanammonium (NMA), and 2-(2-naphthyl)ethanammonium (NEA)) and lead(II) halide (i.e., PbX, X = Cl, Br, and I) frameworks, and their corresponding thin films were fabricated and examined for structure-property relationship. Several new or redetermined crystal structures are reported, including those for (NEA)PbI, (NEA)PbBr, (NMA)PbBr, (PMA)PbBr, and (PEA)PbI. Non-centrosymmetric structures from among these 2D HOIPs were confirmed by piezoresponse force microscopy-especially noteworthy is the structure of (PMA)PbBr, which was previously reported as centrosymmetric. Examination of the impact of organic cation and inorganic layer choice on the exciton absorption/emission properties, among the set of compounds considered, reveals that perovskite layer distortion (i.e., Pb-I-Pb bond angle between adjacent PbI octahedra) has a more global effect on the exciton properties than octahedral distortion (i.e., variation of I-Pb-I bond angles and discrepancy among Pb-I bond lengths within each PbI octahedron). In addition to the characteristic sharp exciton emission for each perovskite, (PMA)PbCl, (PEA)PbCl, (NMA)PbCl, and (PMA)PbBr exhibit separate, broad "white" emission in the long wavelength range. Piezoelectric compounds identified from these 2D HOIPs may be considered for future piezoresponse-type energy or electronic applications.

2D semiconducting metal phosphorus trichalcogenides, particularly the bulk crystals of MPS3 (M = Fe, Mn, Ni, Cd and Zn) sulfides and MPSe3 (M = Fe and Mn) selenides, have been synthesized, crystallized and exfoliated into monolayers. The Raman spectra of monolayer FePS3 and 3-layer FePSe3 show the strong intralayer vibrations and structural stability of the atomically thin layers under ambient condition. The band gaps can be adjusted by element choices in the range of 1.3-3.5 eV. The wide-range band gaps suggest their optoelectronic applications in a broad wavelength range. The calculated cleavage energies of MPS3 are smaller than that of graphite. Therefore, the monolayers used for building of heterostructures by van der Waals stacking could be considered as the candidates for artificial 2D materials with unusual ferroelectric and magnetic properties.

The double perovskite family, A M M X , is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH NH PbI . Given the generally large indirect band gap within most known double perovskites, band-gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs AgBiBr as host, band-gap engineering through alloying of In /Sb has been demonstrated in the current work. Cs Ag(Bi M )Br (M=In, Sb) accommodates up to 75 % In with increased band gap, and up to 37.5 % Sb with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs Ag(Bi Sb )Br . Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed.

Conductive polymer/sulfur composite materials were prepared by heating the mixture of polyacrylonitrile (PAN) and sublimed sulfur. During the heating process, PAN was dehydrogenated by sulfur, forming a conductive main chain similar to polyacetylene. At the same time, the high‐polarity functional group –CN cyclized at the melt state, forming a thermally stable heterocyclic compound in which sulfur was embedded. The nanodispersed composites showed excellent electrochemical properties. Tested as cathode material in a non‐aqueous lithium cell based on poly(vinylidene fluoride) (PVDF) gel electrolyte at room temperature, the composite exhibited a specific capacity up to 850 mA h g–1 in the initial cycle. Its specific capacity remained above 600 mA h g–1 after 50 cycles, about five times that of LiCoO2, and recovered partly after replacement of the anode with a fresh lithium sheet. The utilization of the electrochemically active sulfur was about 90 % assuming a complete reaction to the product, Li2S.

Q. (2016). Raman spectroscopy of atomically thin two-dimensional magnetic iron phosphorus trisulfide (FePS3) crystals. 2D Materials, 3(3), 031009-.