Devices that respond to negligibly small fluctuations in environmental conditions will be of great value for the realization of more sustainable, low-power-consumption actuators and electronic systems. Herein we report an unprecedented film actuator that seemingly operates autonomously, because it responds to the adsorption and desorption of a minute amount of water (several hundred nanograms per 10 mm(2)) possibly induced by fluctuations in the ambient humidity. The actuation is extremely rapid (50 ms for one curl) and can be repeated >10,000 times without deterioration. On heating or light irradiation, the film loses adsorbed water and bends quickly, so that it can jump vertically up to 10 mm from a surface or hit a glass bead. The film consists of a π-stacked carbon nitride polymer, formed by one-pot vapour-deposition polymerization of guanidinium carbonate, and is characterized by a tough, ultralightweight and highly anisotropic layered structure. An actuator partially protected against water adsorption is also shown to walk unidirectionally.

New carbon-based superconductors are synthesized by intercalating metal atoms into the solid-phase hydrocarbons picene and coronene. The highest reported superconducting transition temperature, T(c), of a hydrocarbon superconductor is 18 K for K(3)picene. The physics and chemistry of the hydrocarbon superconductors are extensively described for A(x)picene (A: alkali and alkali earth-metal atoms) for x = 0-5. The theoretical picture of their electronic structure is also reviewed. Future prospects for hydrocarbon superconductors are discussed from the viewpoint of combining electronics with condensed-matter physics: modification of the physical properties of hydrocarbon solids is explored by building them into a field-effect transistor. The features of other carbon-based superconductors are compared to clarify the nature of hydrocarbon superconductors.

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Graphitic carbon nitride (g-CN) has attracted enormous interest in applications as a visible-light-driven photocatalyst, particularly for hydrogen evolution via water splitting. Despite intensive photocatalytic works to achieve higher hydrogen-evolution rate, the chemical and electronic structures that are essential for the water photolysis reactions have not been comprehensibly understood. To reveal the fundamental properties, we utilized well-oriented g-CN films for reliable analyses with several types of electron spectroscopies. Comparing X-ray photoelectron spectra of the g-CN film with those of a g-CN monomer, melem, provided a definite peak assignment of the spectra, from which we identified g-CN as melon. The analysis with ultraviolet photoelectron and inverse photoemission spectroscopy (UPS and IPES) for the melon film clarified energy distributions of the occupied and unoccupied electronic states near the energy gap of melon, respectively. Band structure calculations of a melon crystal revealed orbital characteristics of the electronic states. The calculations also implied that the energy dispersion of only the lowest unoccupied molecular orbital is present along melon chains. The energy structure of melon, determined by the UPS and IPES spectra, was demonstrated to be preferable for water splitting. The results shown in this study will facilitate designs of superior polymeric photocatalysts.

Quantitative modeling demystifies the complex and diverse energetics observed at interfaces between organic semiconductors.

Picene is a phenacene-type aromatic hydrocarbon molecule with five benzene rings. We have fabricated picene single crystal (SC) field-effect transistors (FETs) with solid gate and ionic liquid gate dielectrics. Although the picene SC FET showed a large hole-injection barrier without any modification of interface between source/drain electrodes and picene SC, such a large hole-injection barrier could be effectively reduced by modifying the interface with tetracyanoquinodimethane (TCNQ). Picene SC FET with an HfO2 gate dielectric and TCNQ-coated electrodes shows p-channel characteristics with a smooth hole injection and a field-effect mobility more than 1 cm2 V–1 s–1 in two-terminal measurement. Picene SC FET could be operated even in bottom-contact structure by modifying the interface with octanethiol. Furthermore, picene SC FET operated with ionic liquid gate dielectric, [1-butyl-3-methylimidazolium][hexafluorophosphate], showing the field-effect mobility of 1.8 × 10–1 cm2 V–1 s–1 and low absolute value, 1.9 V, of threshold voltage.

The electronic structure of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) was studied using ultraviolet photoelectron spectroscopy of vapor and thin film and inverse photoemission spectroscopy of thin film. The threshold ionization energy of PCBM was found to be 7.17±0.04 eV in gas phase and 5.96±0.02 eV in solid phase. The threshold electron affinity was 3.9±0.1 eV in solid phase. These values are 0.4−0.6 eV smaller than C60. The density functional theory calculations gave consistent results with these trends and suggested that the electron donation from the side chain to C60 backbone raised the C60-backbone-derived π orbitals of PCBM. The polarization energy of PCBM is 1.21 eV, which is almost the same as C60 but is about 0.5 eV smaller than the value of typical aromatic hydrocarbons.

We have experimentally revealed the band structure and the surface Brillouin zone of insulating picene single crystals (SCs), the mother organic system for a recently discovered aromatic superconductor, with ultraviolet photoelectron spectroscopy (UPS) and low-energy electron diffraction with laser for photoconduction. A hole effective mass of 2.24 m0 and the hole mobility µ h ≥ 9.0 cm 2 /Vs (298 K) were deduced in Γ-Y direction. We have further shown that some picene SCs did not show charging during UPS even without the laser, which indicates that pristine UPS works for high-quality organic SCs.