Chloride Incorporation Process in CH\u3csub\u3e3\u3c/sub\u3eNH\u3csub\u3e3\u3c/sub\u3ePbI\u3csub\u3e3-x\u3c/sub\u3eCl\u3csub\u3ex\u3c/sub\u3e Perovskites via Nanoscale Bandgap Maps

CH3NH3PbI3-xClx perovskites enable fabrication of highly efficient solar cells. Chloride ions benefit the morphology, carrier diffusion length and stability of perovskite films; however, whether those benefits stem from the presence of Cl− in the precursor solution or from their incorporation in annealed films is debated. In this work, the photothermal induced resonance (PTIR), an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH3NH3PbI3-xClx films obtained by a multicycle coating process that produces high efficiency (≈16 %) solar cells. Because chloride ions modify the perovskite lattice, thereby widening the bandgap, measuring the bandgap locally yields the local chloride content. After a mild annealing (60 min, 60°C) the films consist of Cl-rich (x \u3c 0.3) and Cl-poor phases that, upon further annealing (110 °C), evolve into a homogenous Cl-poorer (x \u3c 0.06) phase, suggesting that methylammonium-chrloride is progressively expelled from the film. Despite the small chloride content, CH3NH3PbI3-xClx films show better thermal stability up to 140 °C with respect CH3NH3PbI3 films fabricated with the same methodology

Engineering Near-Field SEIRA Enhancements in Plasmonic Resonators

Engineering of the optical resonances in plasmonic resonator arrays is achieved by virtue of the intrinsic properties of the constituent structures such as composition, size, and shape and by controlling the inter-resonator interactions by virtue of the array’s geometrical arrangement. The nanoscale confinement of the plasmonic field enhances light–matter interactions, enabling, for instance, the surface-enhanced infrared absorption (SEIRA) effect. However, the subwavelength confinement also poses an experimental challenge for discriminating the response stemming from the individual resonators and from the collective response in densely packed arrays. In this work, the photothermal induced resonance technique is leveraged to obtain nanoscale images and spectra of near-field SEIRA hot spots observed in isolated plasmonic resonators of different shapes and in selected resonators within closely packed plasmonic arrays, informing on whether the interactions with neighboring resonators are beneficial or otherwise. Results are correlated with far-field spectra and theoretical calculations

Atomic-scale intermolecular interaction of hydrogen with a single VOPc molecule on the Au(111) surface

Molecular dynamics of hydrogen molecules (H-2) on surfaces and their interactions with other molecules have been studied with the goal of improvement of hydrogen storage devices for energy applications. Recently, the dynamic behavior of a H-2 at low temperature has been utilized in scanning tunnelling microscopy (STM) for sub-atomic resolution imaging within a single molecule. In this work, we have investigated the intermolecular interaction between H-2 and individual vanadyl phthalocyanine (VOPc) molecules on Au(111) substrates by using STM and non-contact atomic force microscopy (NC-AFM). We measured tunnelling spectra and random telegraphic noise (RTN) on VOPc molecules to reveal the origin of the dynamic behavior of the H-2. The tunnelling spectra show switching between two states with different tunnelling conductance as a function of sample bias voltage and RTN is measured near transition voltage between the two states. The spatial variation of the RTN indicates that the two-state fluctuation is dependent on the atomic-scale interaction of H-2 with the VOPc molecule. Density functional theory calculations show that a H-2 molecule can be trapped by a combination of a tip-induced electrostatic potential well and the potential formed by a VOPc underneath. We suggest the origin of the two-state noise as transition of H-2 between minima in these potentials with barrier height of 20-30 meV. In addition, the bias dependent AFM images verify that H-2 can be trapped and released at the tip-sample junction.11Nsciescopu

CH\u3csub\u3e3\u3c/sub\u3eNH\u3csub\u3e3\u3c/sub\u3ePbI\u3csub\u3e3\u3c/sub\u3e perovskites: Ferroelasticity revealed

Ferroelectricity has been proposed as a plausible mechanism to explain the high photovoltaic conversion efficiency in organic-inorganic perovskites; however, convincing experimental evidence in support of this hypothesis is still missing. Identifying and distinguishing ferroelectricity from other properties, such as piezoelectricity, ferroelasticity, etc., is typically nontrivial because these phenomena can coexist in many materials. In this work, a combination of microscopic and nanoscale techniques provides solid evidence for the existence of ferroelastic domains in both CH3NH3PbI3 polycrystalline films and single crystals in the pristine state and under applied stress. Experiments show that the configuration of CH3NH3PbI3 ferroelastic domains in single crystals and polycrystalline films can be controlled with applied stress, suggesting that strain engineering may be used to tune the properties of this material. No evidence of concomitant ferroelectricity was observed. Because grain boundaries have an impact on the long-term stability of organic-inorganic perovskite devices, and because the ferroelastic domain boundaries may differ from regular grain boundaries, the discovery of ferroelasticity provides a new variable to consider in the quest for improving their stability and enabling their widespread adoption

Superstructures of Se adsorbates on Au(111): Scanning tunneling microscopy and spectroscopy study

We studied the geometric and local electronic structure of a Se-adsorbed Au(111) surface. The reconstructed herringbone structure disappeared and the Au(111) surface states were attenuated with Se adsorption on the Au(111) surface, as explained by density functional theory calculations. Electron interference patterns were observed on the exposed Au (111) surface due to electron scattering by potential barriers formed by Se adsorbates. A strong bound state from the Se p-orbital on top of the Se clusters with quantum confinement effects were observed using scanning tunneling microscopy and spectroscopy. © 2019 Published by Elsevier B.V.11sciescopu

Chloride Incorporation Process in CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> Perovskites via Nanoscale Bandgap Maps

CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> perovskites enable fabrication of highly efficient solar cells. Chloride ions benefit the morphology, carrier diffusion length, and stability of perovskite films; however, whether those benefits stem from the presence of Cl^– in the precursor solution or from their incorporation in annealed films is debated. In this work, the photothermal-induced resonance, an in situ technique with nanoscale resolution, is leveraged to measure the bandgap of CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> films obtained by a multicycle coating process that produces high efficiency (∼16%) solar cells. Because chloride ions modify the perovskite lattice, thereby widening the bandgap, measuring the bandgap locally yields the local chloride content. After a mild annealing (60 min, 60 °C) the films consist of Cl-rich (<i>x</i> < 0.3) and Cl-poor phases that upon further annealing (110 °C) evolve into a homogeneous Cl-poorer (<i>x</i> < 0.06) phase, suggesting that methylammonium-chrloride is progressively expelled from the film. Despite the small chloride content, CH₃NH₃PbI_3–<i>x</i>Cl_<i>x</i> films show better thermal stability up to 140 °C with respect CH₃NH₃PbI₃ films fabricated with the same methodology

Nanoscale imaging and spectroscopy of plasmonic modes with the PTIR technique

The photothermal induced resonance (PTIR) method measures the near-field absorption in gold plasmonic structures. PTIR absorption images show the interference between the bright and dark modes of asymmetric split ring resonators (ASRRs). The plasmonic absorption spectra of the ASRRs individual arcs are obtained locally, confirming the collective nature of the plasmonic excitation. Scale bars are 500 nm

Selective resolution of phonon modes in STM-IETS on clean and oxygen-adsorbed Cu(100) surfaces

The observation of surface phonon using scanning probe microscopy can provide important information related to local structural and electrical properties. In this study, surface phonon modes on a Cu(100) surface were measured using inelastic tunneling spectroscopy of scanning tunneling microscopy. One phonon mode was measured at 3.6 meV on a clean Cu(100) surface. On an oxygen-adsorbed Cu(100) surface, another phonon mode was measured at 13.5 meV. This phonon mode was considered to be enhanced by the symmetry created by Cu-missing rows. The spatially varying d2I/dV2 map showed the effect of surface stress relaxation.© 2019 Published by Elsevier B.V.11sciescopu