Charges accumulated in an electric double layer (EDL) play key roles in various interfacial phenomena and electronic devices. However, direct imaging of their spatial distribution has been a great challenge, which has hindered our nano-level understanding of the mechanisms of such interfacial phenomena and functions. In this study, we present direct imaging of charges accumulated at an electrode-electrolyte interface using three-dimensional open-loop electric potential microscopy (3D-OL-EPM). Conventional OL-EPM allows us to visualize two-dimensional potential distributions in liquid yet the zero of the measured potential is not well defined due to the influence of the long-range (LR) interaction between the cantilever and the sample. Here, we present practical ways to reduce such an influence by improving the equation for the potential calculation and subtracting the LR contribution estimated from a Z potential profile. These improvements enabled the calibration of the measured potential values with respect to the bulk solution potential. With these improvements, we visualized opposite charge accumulation behaviors on a polarizable and non-polarizable electrode with a varying electrode potential. Combining OL-EPM with a 3D tip scanning method, we also performed a 3D-OL-EPM measurement on a Cu fine wire and visualized the nanoscale distribution of the charges accumulated at the interface. Such real-space information on the charge distributions in an EDL should provide valuable insights into the mechanisms of interfacial phenomena and functions that are important in various academic and industrial research on electronic devices, electrochemistry, tribology and life sciences.

No abstract

Understanding the mechanisms of self-organization of short peptides into two- and three-dimensional architectures are of great interest in the formation of crystalline biomolecular systems and their practical applications. Since the assembly is a dynamic process, the study of structural development is challenging at the submolecular dimensions continuously across an adequate time scale in the natural biological environment, in addition to the complexities stemming from the labile molecular structures of short peptides. Self-organization of solid binding peptides on surfaces offers prospects to overcome these challenges. Here we use a graphite binding dodecapeptide, GrBP5, and record its self-organization process of the first two layers on highly oriented pyrolytic graphite surface in an aqueous solution by using frequency modulation atomic force microscopy in situ. The observations suggest that the first layer forms homogeneously, generating self-organized crystals with a lattice structure in contact with the underlying graphite. The second layer formation is mostly heterogeneous, triggered by the crystalline defects on the first layer, growing row-by-row establishing nominally diverse biomolecular self-organized structures with transient crystalline phases. The assembly is highly dependent on the peptide concentration, with the nucleation being high in high molecular concentrations, e.g., >100 μM, while the domain size is small, with an increase in the growth rate that gradually slows down. Self-assembled peptide crystals are composed of either singlets or doublets establishing P1 and P2 oblique lattices, respectively, each commensurate with the underlying graphite lattice with chiral crystal relations. This work provides insights into the surface behavior of short peptides on solids and offers quantitative guidance toward elucidating molecular mechanisms of self-assembly helping in the scientific understanding and construction of coherent bio/nano hybrid interfaces.

Layered perovskite oxyhalides Bi4MO8X (M = Nb, Ta; X = Cl, Br) are promising visible-light photocatalysts for water splitting, where the polar structure may enhance the conductivity of photocarriers. In this study, the domain structure of Bi4NbO8Br single crystal was investigated using piezoresponse force microscopy and transmission electron microscope. We observed a rare domain structure with a ferroelectric 180° domain in the nanoscale ferroelastic 90° domains developed in the ab plane. We also discuss the effect of these domain structures on the dynamics of photocarriers, which may provide new ideas for the design of highly active photocatalyst.

A molecular-scale understanding of self-assembled monolayers (SAMs) of sulfonate-terminated alkanethiols is crucial for interfacial studies of functionalized SAMs and their various applications. However, such an understanding has been difficult to achieve because of the lack of direct information on these molecular-scale structures in real space. In this study, we investigated the structures of sulfonate SAMs of sodium 11-mercapto-1-undecanesulfonate (MUS) by frequency modulation atomic force microscopy (FM-AFM) in liquid. The subnanometer-resolution FM-AFM images showed that the single-component MUS SAM prepared in pure water had random surface structures. In contrast, the MUS SAM prepared in a water-ethanol mixed solvent showed periodic striped structures with a flat-lying conformation. The results suggest a significant solvent effect on molecular-scale structures of long-chain sulfonate SAMs. In addition, we investigated the molecular-scale structures of mixed SAMs of MUS and 11-mercapto-1-undecanol (MUO) with alkane chains of the same length. The FM-AFM images of the mixed SAMs showed clear phase separation between MUS SAM and MUO SAM domains. In the MUO SAM domains, the incorporated MUS molecules appeared as protrusions. The results obtained in this study provide direct structural information on long-chain sulfonate and mixed SAMs.