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Nanoscale observation of charge distribution and electric polarization is crucial for understanding and controlling functional materials and devices. In particular, the importance of charge dynamics is well recognized, and direct methods to observe charge generation, transfer, and recombination processes are required. Here, we describe tip-synchronized time-resolved electrostatic force microscopy. Numerical modeling clarifies that the tip-synchronized method provides temporal resolution with the timescale of the cantilever oscillation cycle. This method enables us to resolve sub-microsecond charge migration on the surface. The recombination of photo-excited carriers in a bilayer organic photovoltaic thin film is observed as a movie with a 0.3 µs frame step time resolution. Analysis of the images shows that the carrier lifetime is 2.3 µs near the donor/acceptor interface. The tip-synchronized method increases the range of time-resolved electrostatic force microscopy, paving the way for studies of nanoscale charge dynamics. An understanding of charge dynamics and direct observations of charge generation, transfer and recombination is important to help develop and apply various materials for electronic devices. The authors develop a time-resolved electrostatic force microscopy technique to visually observe charge migration on the nanoscale at a sub-microsecond timeframe.

Although NH3 has recently been regarded as a renewable and carbon-free energy source, NH3 fuel has a high ignition temperature and its use results in the production of N2O/NOx. To overcome these issues, in this work, we focused on a novel catalytic combustion system and copper oxides (CuOx) catalysts supported on aluminum silicates (Al6O13Si2, 3Al2O3·2SiO2, 3A2S) and silicon oxides (SiO2). The preparation methods for 3A2S as a support material were optimized to achieve high catalytic NH3 combustion activity and high N2 (low N2O/NO) selectivity. Because the CuOx supported on 3A2S prepared by an alkoxide method and subsequent calcination at 1200 °C for 5 h in air exhibited high catalytic performance for NH3 combustion, the properties of the catalyst in addition to CuOx/SiO2 thermally aged at 900 °C for 100 h in air were also evaluated using high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray mapping, operando X-ray absorption fine structure analysis, X-ray photoelectron spectroscopy, and gas adsorption techniques. Our findings suggest that the catalytic NH3 combustion activity, NO selectivity, and N2O selectivity are closely associated with the reducibility (dispersion) of CuOx, local structures around Cu, fraction of the oxidation state (Cu2+), and adsorption species of NH3 (NH, imide). Finally, we propose a reaction mechanism for catalytic NH3 combustion over not only CuOx/3A2S but also CuOx/SiO2.

We study the catalytic combustion properties of supported and unsupported manganese oxides (MnOx) with NH3 (a carbon-free energy source). Unsupported MnOx with higher oxidation states tends to exhibit higher catalytic NH3 combustion activity (MnO2 > Mn2O3 > MnO). X-ray diffractometry (XRD) and absorption fine structure (XAFS) analysis show that MnO2 reduces to Mn2O3 after the combustion reaction. Among the MnOx (5 wt% Mn) supported on various materials, MnOx/CeO2 exhibited the highest activity. Analysis of XPS (X-ray photoelectron spectroscopy) spectra before and after the reaction suggests that the oxidation state of CeO2-supported MnOx is a mixture of Mn2 + and Mn3 +.

Recently, NH3 has been thought to be a renewable and carbon-free energy source. The use of NH3 fuel, however, is hindered by its high ignition temperature and N2O/NO production. To overcome these issues, in this study, the combustion of NH3 over copper oxide (CuOx) and platinum (Pt) catalysts supported on aluminium silicates (3Al2O3·2SiO2), aluminium oxides (Al2O3), and silicon oxides (SiO2) were compared. To achieve high catalytic activity for the combustion of NH3 and high selectivity for N2 (or low selectively for N2O/NO), conditions for the preparation of impregnated binary catalysts were optimised. With respect to the binary catalysts, sequentially impregnated CuOx/Pt/Al2O3 exhibited relatively higher activity, N2 selectivity, and thermal stability. From XRD and XAFS analyses, CuOx and Pt in CuOx/Pt/Al2O3 were present as CuAl2O4 and metallic Pt, respectively. Given that the combustion activity was closely associated with the Pt nanoparticle size, which was estimated from the Scherrer equation and the pulsed CO technique, highly dispersed Pt nanoparticles were crucial for the low-temperature light-off of NH3. For single and binary catalysts, although NH (imide) deformation modes as a key species for N2O production were detected by in situ FTIR spectral analysis, the band intensity of CuOx/Pt/Al2O3 was less than those of CuOx/Al2O3 and Pt/Al2O3. Therefore, CuOx/Pt/Al2O3 exhibits high selectivity for N2 in NH3 combustion.

We present the formation of a complex molecular network consisting of highly water soluble λ-DNA and a redox protein, Cytochrome c (Cyt c), at the air–water interface by Langmuir–Blodgett technique. Time dependent adsorption of these materials and the formation of a Cyt c/λ-DNA complex interfacial layer in the Langmuir trough were systematically studied by recording surface pressure versus trough area isotherms after various subphase incubation times. We have succeeded in separating two effects: one is the phase change of the monolayers and the other is the number of molecules participating in the monolayer formation with the change in incubation time using a normalized isotherm in units of critical surface area. The interaction in the complex monolayer was found to be same as that of single component λ-DNA during 3 h of subphase incubation. However, it was also similar to that of a single component Cyt c monolayer after 5 h incubation. The morphology and electrical polarizations of these interfacial films deposited onto a mica substrate were analyzed by Atomic Force Microscopy and electrostatic force microscopy respectively. It was found that Cyt c and λ-DNA immediately form the complex network at the air–water interface, and change to rod-like large aggregates with prolonged incubation.

Nonlinear current–voltage (I–V) characteristics is an important property for the realization of information processing in molecular electronics. We studied the electrical conduction through a Ru–dye complex (N-719) on a 2-aminoethanethiol (2-AET) monolayer in a nanoparticle bridge junction system. The nonlinear I–V characteristics exhibited a threshold voltage at around 1.2 V and little temperature dependence. From the calculation of the molecular states using density functional theory and the energy alignment between the electrodes and molecules, the conduction mechanism in this system was considered to be resonant tunneling via the HOMO level of N-719. Our results indicate that the weak electronic coupling of electrodes and molecules is essential for obtaining nonlinear I–V characteristics with a clear threshold voltage that reflect the intrinsic molecular state.

The localized charge and electrostatic properties of organic photovoltaic thin films are predominating factors for controlling energy conversion efficiency. The surface potential and electrostatic structures of organic photovoltaic thin films were investigated by frequency shift mode Kelvin force microscopy (KFM) and electrostatic force microscopy (EFM). The KFM images of a poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene]/phenyl-C61-butyric-acid-methyl ester (PCBM) blend thin film reveals that the PCBM domains precipitate as the topmost layer on the thin films. We find fine structures that were not observed in the topography and KFM images. The bias dependence of the EFM images suggests that the EFM contrast reflects the field-induced polarization, indicating the presence of charge trapping sites.