Nonlinear Phase Imaging of Gold Nanoparticles Embedded in Organic Thin Films.

The phase detection in the dynamic mode of the atomic force microscopes is a known technique for mapping nanoscale surface heterogeneities. We present here an additional functionality of this technique, which allows high-resolution imaging of embedded inorganic nanoparticles with diameter and interparticle distances of a few nanometers. The method is based on a highly nonlinear tip-sample interaction occurring markedly above the nanoparticles, giving thus a high phase contrast between zones with and without nanoparticles. A relationship between the tip-sample interaction strength and the phase signal is established in experiments and from calculations conducted with the model developed by Haviland et al. [ Soft Matter 2016 , 12 , 619 ], which is based on solving a combined equation of motion for both the cantilever and surface while taking into account the time-varying interaction forces. The nonlinear phase behavior at the origin of the subnanometer spatial resolution is found by numerical analyses to be the result of a local mechanical stiffening of the zone containing nanoparticles, which is enhanced by 2 orders of magnitude or more.

Design of Nanostructured Hybrid Electrodes Based on a Liquid Crystalline Zn(II) Coordination Complex-Carbon Nanotubes Composition for the Specific Electrochemical Sensing of Uric Acid.

A metallomesogen based on an Zn(II) coordination complex was employed as precursor to obtain a complex matrix nanoplatform for the fabrication of a high-performance electrochemical hybrid sensor. Three representative paste electrodes, which differ by the weight ratio between Zn(II) metallomesogen and carbon nanotubes (CNT), i.e., PE_01, PE_02 and PE_03, were obtained by mixing the materials in different amounts. The composition with the largest amount of CNT with respect to Zn complex, i.e., PE_03, gives the best electrochemical signal for uric acid detection by cyclic voltammetry in an alkaline medium. The amphiphilic structure of the Zn(II) coordination complex likely induces a regular separation between the metal centers favoring the redox system through their reduction, followed by stripping, and is characterized by enhanced electrocatalytic activity towards uric acid oxidation. The comparative detection of uric acid between the PE_03 paste electrode and the commercial zinc electrode demonstrated the superiority of the former, and its great potential for the development of advanced electrochemical detection of uric acid. Advanced electrochemical techniques, such as differential-pulsed voltammetry (DPV) and square-wave voltammetry (SWV), allowed for the highly sensitive detection of uric acid in aqueous alkaline solutions. In addition, a good and fast amperometric signal for uric acid detection was achieved by multiple-pulsed amperometry, which was validated by urine analysis.

Correlative Microscopy Insight on Electrodeposited Ultrathin Graphite Oxide Films.

Here, we present a correlative microscopic analysis of electrodeposited films from catechol solutions in aqueous electrolytes. The films were prepared in a miniaturized electrochemical cell and were analyzed by identical location transmission electron microscopy, scanning transmission X-ray microscopy, and atomic force microscopy. Thanks to this combined approach, we have shown that the electrodeposited films are constituted of ultrathin graphite oxide nanosheets. Detailed information about the electronic structure of the films was obtained by X-ray absorption near edge structure spectroscopy. These results show the large potential of soft electrochemical conditions for the bottom-up production of ultrathin graphite oxide nanosheet films via a one-pot green chemistry approach from simple organic building blocks.

Tuning photovoltaic response in Bi2FeCrO6 films by ferroelectric poling.

Ferroelectric materials are interesting candidates for future photovoltaic applications due to their potential to overcome the fundamental limits of conventional single bandgap semiconductor-based solar cells. Although a more efficient charge separation and above bandgap photovoltages are advantageous in these materials, tailoring their photovoltaic response using ferroelectric functionalities remains puzzling. Here we address this issue by reporting a clear hysteretic character of the photovoltaic effect as a function of electric field and its dependence on the poling history. Furthermore, we obtain insight into light induced nonequilibrium charge carrier dynamics in Bi2FeCrO6 films involving not only charge generation, but also recombination processes. At the ferroelectric remanence, light is able to electrically depolarize the films with remanent and transient effects as evidenced by electrical and piezoresponse force microscopy (PFM) measurements. The hysteretic nature of the photovoltaic response and its nonlinear character at larger light intensities can be used to optimize the photovoltaic performance of future ferroelectric-based solar cells.

Two dimensional dipolar coupling in monolayers of silver and gold nanoparticles on a dielectric substrate.

The dimensionality of assembled nanoparticles plays an important role in their optical and magnetic properties, via dipolar effects and the interaction with their environment. In this work we develop a methodology for distinguishing between two (2D) and three (3D) dimensional collective interactions on the surface plasmon resonance of assembled metal nanoparticles. Towards that goal, we elaborate different sets of Au and Ag nanoparticles as suspensions, random 3D arrangements and well organized 2D arrays. Then we model their scattering cross-section using effective field methods in dimension n, including interparticle as well as particle-substrate dipolar interactions. For this modelling, two effective field medium approaches are employed, taking into account the filling factors of the assemblies. Our results are important for realizing photonic amplifier devices.

Chiral Conformation at a Molecular Level of a Propeller-Like Open-Shell Molecule on Au(111).

A key stage in engineering molecular functional organizations is represented by controlling the supramolecular assembly of single molecular building blocks, tectons, into ordered networks. Here, we show how an open-shell, propeller-like molecule has been deposited under UHV conditions on Au(111) and its supramolecular organization characterized by scanning tunneling microscopy (STM). Racemic islands were observed at room temperature, and their chirality was imaged at the molecular level at low temperature. Modeling further suggests that the observed chirally alternating ordering dominated by intermolecular interactions is energetically favored. Electron paramagnetic resonance and ultraviolet photoemission spectroscopy evidences suggest that the supramolecular networks may preserve the open-shell character of the tecton. These results represent a fundamental step forward toward the engineering of purely organic spintronic devices.