Etsushi Tsuji

Fabrication of superoleophobic hierarchical surfaces for low-surface-tension liquids

This study demonstrates the fabrication of hierarchical surfaces with super-repellency even for low-surface-tension liquids, including octane (surface tension of 21.7 mN m−1). Dual-pore surfaces were prepared by a combination of practical wet processes on an aluminium substrate: chemical etching, anodizing, and organic monolayer coating. The size of the larger pores formed by the chemical etching of aluminium is controlled by the concentration of HCl in the CuCl2/HCl etching solution. The etched aluminium is then anodized to introduce nanopores, followed by a pore-widening treatment that controls the nanopore size and porosity. The repellency for low-surface-tension liquids is enhanced by increasing the size of the larger pores as well as the porosity of the walls of the larger pores in this dual-pore morphology. Under optimized morphology with a fluoroalkyl-phosphate monolayer coating, an advancing contact angle close to 160°, a contact angle hysteresis of less than 5° and a sliding angle of 10° is achieved even for octane.

Low-Temperature Oxygen Storage of CrIV–CrV Mixed-Valence YCr1–xPxO4−δ Driven by Local Condensation around Oxygen-Deficient Orthochromite

The oxygen storage capability and related defect structure of tetrahedral orthochromite(V) compound YCr1-xPxO4 (x = 0, 0.3, 0.5, and 0.7) were investigated by employing thermal gravimetry and in situ X-ray spectroscopy for reversible oxygen store/release driven by heating-cooling cycles in the temperature range from 50 to 600 °C. YCr1-xPxO4 started releasing oxygen as heated from 50 °C under ambient atmosphere, with reduction of CrV to CrIV, while the reduced YCr1-xPxO4-δ phase was significantly reoxidized via absorbing oxygen by cooling to 50 °C under ambient atmosphere, recovering the original stoichiometric phase. Operando X-ray adsorption spectroscopy and first-principles calculations demonstrate that nonstoichiometric YCr1-xPxO4-δ phases were stabilized by forming linking polyhedral CrIV2O76- via corner sharing between oxygen-deficient CrIVO32- and adjacent CrIVO44-. YCr1-xPxO4 was found to have an extremely low reduction enthalpy of about 20 kJ mol-1 probably due to the relatively high reduction potential of high-valence-state Cr(V)/Cr(IV) redox pairs, thereby resulting in reversible oxygen storage in such a low-temperature region.

Fabrication of a resistive switching gallium oxide thin film with a tailored gallium valence state and oxygen deficiency by rf cosputtering process

Resistive switching gallium oxide base thin films with tailored oxygen deficiency were fabricated by rf cosputtering of Ga2O3 and Cr. XPS and STEM-EDX analyses were used to determine that the resultant film was made of a homogeneous oxide glass layer with mixed valance states of Ga(III)–Ga(I). The amount of Ga(I) and the corresponding oxygen deficiency was precisely controlled because the following redox reaction subsequently progresses within the deposited films: 3Ga(III) + 2Cr(0) → 3Ga(I) + 2Cr(III). The on/off resistance ratio was largely varied by changing the Ga(I) fraction in relation to the oxide ion conductivity, and Ga0.82Cr0.18O1.2 thin film was found to exhibit an optimal switching performance. The film resistance state was tunable by 100s of μs pulse biasing and was incrementally changed by increasing the applied pulse numbers. The strongly time-dependent switching events and area dependent current level of Cr-GaOx films were distinct from the abrupt switching behavior of the filamentary mechanism TiOx thin film devices. It was demonstrated that rf cosputtering of the metal oxides and the corresponding oxygen scavenging metals was a powerful technique to design the bulk state resistive switching devices based on nonstoichiometric metal oxide thin films.

Enhanced hydrogen permeability of hafnium nitride nanocrystalline membranes by interfacial hydride conduction

Hydrogen permeability based on mixed hydride ion electron conduction was demonstrated for hafnium nitride HfNx (film thickness of 100–500 nm, x = 0.8 and 1.0) nanocrystalline membranes. Nanocrystalline films with a (100) orientation and crystallite sizes of a few tens of nanometers were prepared on porous alumina supports by radio frequency (RF) reactive sputtering. Combined spectroscopic, permeability, and microbalance analysis suggests that the nanocrystalline matrices were readily hydrogenated by the formation of Hf–H terminal groups on the internal grain surfaces at ambient temperature and thus efficient hydrogen permeation took place due to an enhanced diffusion of hydridic defects through the grain boundaries; this was further aided by the Hf–H bond exchange process. Hence, membranes with an average crystallite size of 11 nm yielded a hydrogen flux of 6 × 10−7 mol cm−2 s−1 at 25 °C at an applied hydrogen partial pressure of 50 kPa; this value is higher than those exhibited by the current state-of-the-art Pd membranes. These findings establish a new concept for Pd alternatives based on the pronounced hydric conductivity of transition metal nitride nanomaterials.

Direct Methylation of Benzene with Methane Catalyzed by Co/MFI Zeolite

Cobalt‐loaded MFI zeolite showed distinct activity for direct methylation of benzene with methane into toluene. High activity was found at around 0.6 of Co/Al molar ratio. Incorporation of carbon from methane into the methyl group of toluene was confirmed with isotope tracer experiments and mass spectroscopy. Ammonia infrared‐mass spectroscopy temperature‐programmed desorption, transmission electron microscopy, X‐ray absorption near edge spectroscopy and extended X‐ray absorption fine structure indicated that Lewis acidic divalent (+II of oxidation state) Co species mono‐atomically dispersed on the ion exchange site of MFI zeolite was the active species.