The fabrication of multidimensional organometallic halide perovskite via a low‐pressure vapor‐assisted solution process is demonstrated for the first time. Phenyl ethyl‐ammonium iodide (PEAI)‐doped ...lead iodide (PbI2) is first spin‐coated onto the substrate and subsequently reacts with methyl‐ammonium iodide (MAI) vapor in a low‐pressure heating oven. The doping ratio of PEAI in MAI‐vapor‐treated perovskite has significant impact on the crystalline structure, surface morphology, grain size, UV–vis absorption and photoluminescence spectra, and the resultant device performance. Multiple photoluminescence spectra are observed in the perovskite film starting with high PEAI/PbI2 ratio, which suggests the coexistence of low‐dimensional perovskite (PEA2MAn−1PbnI3n+1) with various values of n after vapor reaction. The dimensionality of the as‐fabricated perovskite film reveals an evolution from 2D, hybrid 2D/3D to 3D structure when the doping level of PEAI/PbI2 ratio varies from 2 to 0. Scanning electron microscopy images and Kelvin probe force microscopy mapping show that the PEAI‐containing perovskite grain is presumably formed around the MAPbI3 perovskite grain to benefit MAPbI3 grain growth. The device employing perovskite with PEAI/PbI2 = 0.05 achieves a champion power conversion efficiency of 19.10% with an open‐circuit voltage of 1.08 V, a current density of 21.91 mA cm−2, and a remarkable fill factor of 80.36%.
A high‐efficiency perovskite solar cell using 2D/3D hybrid perovskite prepared by a low‐pressure vapor‐assisted solution process is demonstrated. Phenyl ethyl‐ammonium iodide (PEAI)‐containing 2D perovskite forms around the MAPbI3 perovskite grain and is beneficial for MAPbI3 grain growth. The optimized device employing perovskite with PEAI/PbI2 = 0.05 achieves a promising power conversion efficiency of 19.10% with an open‐circuit voltage of 1.08 V.
The emergence of two-dimensional electronic materials has stimulated proposals of novel electronic and photonic devices based on the heterostructures of transition metal dichalcogenides. Here we ...report the determination of band offsets in the heterostructures of transition metal dichalcogenides by using microbeam X-ray photoelectron spectroscopy and scanning tunnelling microscopy/spectroscopy. We determine a type-II alignment between MoS2 and WSe2 with a valence band offset value of 0.83 eV and a conduction band offset of 0.76 eV. First-principles calculations show that in this heterostructure with dissimilar chalcogen atoms, the electronic structures of WSe2 and MoS2 are well retained in their respective layers due to a weak interlayer coupling. Moreover, a valence band offset of 0.94 eV is obtained from density functional theory, consistent with the experimental determination.
Characterizing the chemistry and magnetism of magnetotactic bacteria (MTB) is an important aspect of understanding the biomineralization mechanism and function of the chains of magnetosomes (Fe₃O₄ ...nanoparticles) found in such species. Images and X-ray absorption spectra (XAS) of magnetosomes extracted from, and magnetosomes in, whole Magnetovibrio blakemorei strain MV-1 cells have been recorded using soft X-ray ptychography at the Fe 2p edge. A spatial resolution of 7 nm is demonstrated. Precursor-like and immature magnetosome phases in a whole MV-1 cell were visualized, and their Fe 2p spectra were measured. Based on these results, a model for the pathway of magnetosome biomineralization for MV-1 is proposed. Fe 2p X-ray magnetic circular dichroism (XMCD) spectra have been derived from ptychography image sequences recorded using left and right circular polarization. The shape of the XAS and XMCD signals in the ptychographic absorption spectra of both sample types is identical to the shape and signals measured with conventional bright-field scanning transmission X-ray microscope. A weaker and inverted XMCD signal was observed in the ptychographic phase spectra of the extracted magnetosomes. The XMCD ptychographic phase spectrum of the intracellular magnetosomes differed from the ptychographic phase spectrum of the extracted magnetosomes. These results demonstrate that spectro-ptychography offers a superior means of characterizing the chemical and magnetic properties of MTB at the individual magnetosome level.
X‐ray circular dichroism, arising from the contrast in X‐ray absorption between opposite photon helicities, serves as a spectroscopic tool to measure the magnetization of ferromagnetic materials and ...identify the handedness of chiral crystals. Antiferromagnets with crystallographic chirality typically lack X‐ray magnetic circular dichroism because of time‐reversal symmetry, yet exhibit weak X‐ray natural circular dichroism. Here, the observation of giant natural circular dichroism in the Ni L3‐edge X‐ray absorption of Ni3TeO6 is reported, a polar and chiral antiferromagnet with effective time‐reversal symmetry. To unravel this intriguing phenomenon, a phenomenological model is proposed that classifies the movement of photons in a chiral crystal within the same symmetry class as that of a magnetic field. The coupling of X‐ray polarization with the induced magnetization yields giant X‐ray natural circular dichroism, revealing typical ferromagnetic behaviors allowed by the symmetry in an antiferromagnet, i.e., the altermagnetism of Ni3TeO6. The findings provide evidence for the interplay between magnetism and crystal chirality in natural optical activity. Additionally, the first example of a new class of magnetic materials exhibiting circular dichroism is established with time‐reversal symmetry.
The article reveals a new type of altermagnet, in which the symmetry allows for typical ferromagnetic behaviors. It presents X‐ray circular dichroism observed in a chiral antiferromagnet with time‐reversal symmetry. This phenomenon contrasts conventional X‐ray magnetic circular dichroism. As X‐rays propagate through the material, the Berry curvature, arising from the inversion symmetry breaking, gives rise to distinct circular dichroism.
Polymer electrolyte membrane fuel cells (PEMFCs) are a promising and sustainable alternative to internal combustion engines for automotive applications. Polymeric perfluorosulfonic acid (PFSA) plays ...a key role in PEMFCs as a proton conductor in the anode and cathode catalyst layers and in the electrolyte membrane. In this study, spectroscopic scanning coherent diffraction imaging (spectro-ptychography) and spectro-ptychographic tomography were used to quantitatively image PFSA ionomers in PEMFC cathodes in both two and three dimensions. We verify that soft X-ray ptychography gives significant spatial resolution improvement on soft matter polymeric materials. A two-dimensional spatial resolution of better than 15 nm was achieved. With better detectors and brighter and more coherent X-ray beams, radiation-sensitive PFSA ionomers will be visualized with acceptable levels of chemical and structural modification. This work is a step toward visualization of ionomers in PEMFC cathodes at high spatial resolution (presently sub-15 nm, but ultimately below 10 nm), which will be transformative with respect to optimization of PEMFCs for automotive use.
Surfaces of semiconductors with strong spin-orbit coupling are of great interest for use in spintronic devices exploiting the Rashba effect. BiTeI features large Rashba-type spin splitting in both ...valence and conduction bands. Either can be shifted towards the Fermi level by surface band bending induced by the two possible polar terminations, making Rashba spin-split electron or hole bands electronically accessible. Here we demonstrate the first real-space microscopic identification of each termination with a multi-technique experimental approach. Using spatially resolved tunnelling spectroscopy across the lateral boundary between the two terminations, a previously speculated on p-n junction-like discontinuity in electronic structure at the lateral boundary is confirmed experimentally. These findings realize an important step towards the exploitation of the unique behaviour of the Rashba semiconductor BiTeI for new device concepts in spintronics.
We present a generic and efficient chemical patterning method based on local plasma-induced conversion of surface functional groups on self-assembled monolayers (SAMs). Here, spatially controlled ...plasma exposure is realized by elastomeric poly(dimethylsiloxane) (PDMS) contact masks or channel stamps with feature sizes ranging from nanometer, micrometer, to centimeter. This chemical conversion method has been comprehensively characterized by a set of techniques, including contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), scanning electron microscopy (SEM), and scanning Kelvin probe microscopy (SKPM). In particular, XPS and SPEM can be used to distinguish regions of different surface functionalities and elucidate the mechanism of plasma-induced chemical conversion. In the case of an octadecyltrichlorosilane (OTS) monolayer, we show that exposure to low-power air plasma causes hydroxylation and oxidation of the methyl terminal group on an OTS-covered Si surface and generates polar functional groups such as hydroxyl, aldehylde, and carboxyl groups, which can allow subsequent grafting of dissimilar SAMs and adsorption of colloid nanoparticles onto the patterned areas with an achievable resolution down to the 50 nm range.
The range of mechanically cleavable Van der Waals crystals covers materials with diverse physical and chemical properties. However, very few of these materials exhibit magnetism or magnetic order, ...and thus the provision of cleavable magnetic compounds would supply invaluable building blocks for the design of heterostructures assembled from Van der Waals crystals. Here we report the first successful isolation of monolayer and few-layer samples of the compound nickel phosphorus trisulfide (NiPS3) by mechanical exfoliation. This material belongs to the class of transition metal phosphorus trisulfides (MPS3), several of which exhibit antiferromagnetic order at low temperature, and which have not been reported in the form of ultrathin sheets so far. We establish layer numbers by optical bright field microscopy and atomic force microscopy, and perform a detailed Raman spectroscopic characterization of bilayer and thicker NiPS3 flakes. Raman spectral features are strong functions of excitation wavelength and sample thickness, highlighting the important role of interlayer coupling. Furthermore, our observations provide a spectral fingerprint for distinct layer numbers, allowing us to establish a sensitive and convenient means for layer number determination.
In this study, various concentrations of the large-sized cation iodide, namely, phenylethylammonium iodide (PEAI), incorporated in lead iodide (PbI2) solid films react with heated methylammonium ...iodide (MAI) to fabricate 2D/3D mixed perovskite films with vertical phase distribution, which are prepared by the low-pressure vapor-assisted solution process (LP-VASP). The 2D/3D mixed perovskite films exhibit multiple photoluminescence (PL) emissions that correspond to a 2D Ruddlesden–Popper layered perovskite of PEA2MA n–1Pb n X3n+1 with varying n values and a 3D MAPbI3 perovskite. Their crystalline structure along with crystal orientation, surface morphology, and surface potential is examined by X-ray diffraction, grazing-incidence wide-angle X-ray scattering, and Kelvin probe force microscopy, respectively. Confocal PL microscopy, two-photon excitation microscopy, and scanning transmission X-ray microscopy are further conducted to map the spatial and energy spectral distribution of 2D layered perovskites in the resultant film. From these results, multiple 2D layered perovskites are presumably formed in the bulk, while a 3D perovskite is mainly produced on the surface. The dimensional variation across the vapor-treated film is attributed to the phenylethylamine vapor (PEA(g)) evaporating from the PEAI-added PbI2 film and the methylamine vapor (MA(g)) reaction with the PEAI-added PbI2 film initiated from the film surface. A gradient phase distribution from 2D (bottom) to 3D (surface) perovskites is intuitively fabricated.
PDF
