Highly stable Fe/CeO2 catalyst for the reverse water gas shift reaction in the presence of H2S.

This study focused on evaluating the catalytic properties for the reverse water gas shift reaction (RWGS: CO2 + H2 → CO + H2O ΔH 0 = 42.1 kJ mol-1) in the presence of hydrogen sulfide (H2S) over a Fe/CeO2 catalyst, commercial Cu-Zn catalyst for the WGS reaction (MDC-7), and Co-Mo catalyst for hydrocarbon desulfurization. The Fe/CeO2 catalyst exhibited a relatively high catalytic activity to RWGS, compared to the commercial MDC-7 and Co-Mo catalysts. In addition, the Fe/CeO2 catalyst showed stable performance in the RWGS environment that contained high concentrations of H2S. The role of co-feeding H2S was investigated over the Fe/CeO2 catalyst by the temperature programmed reaction (TPR) of CO2 and H2 in the presence of H2S. The result of TPR indicated that the co-feeding H2S might enhance RWGS performance due to H2S acting as the hydrogen source to reduce CO2.

Electron aspirator using electron-electron scattering in nanoscale silicon.

Current enhancement without increasing the input power is a critical issue to be pursued for electronic circuits. However, drivability of metal-oxide-semiconductor (MOS) transistors is limited by the source-injection current, and electrons that have passed through the source unavoidably waste their momentum to the phonon bath. Here, we propose the Si electron-aspirator, a nanometer-scaled MOS device with a T-shaped branch, to go beyond this limit. The device utilizes the hydrodynamic nature of electrons due to the electron-electron scattering, by which the injected hot electrons transfer their momentum to cold electrons before they relax with the phonon bath. This momentum transfer induces an electron flow from the grounded side terminal without additional power sources. The operation is demonstrated by observing the output-current enhancement by a factor of about 3 at 8 K, which reveals that the electron-electron scattering can govern the electron transport in nanometer-scaled MOS devices, and increase their effective drivability.

Single-electron thermal noise.

We report the observation of thermal noise in the motion of single electrons in an ultimately small dynamic random access memory (DRAM). The nanometer-scale transistors that compose the DRAM resolve the thermal noise in single-electron motion. A complete set of fundamental tests conducted on this single-electron thermal noise shows that the noise perfectly follows all the aspects predicted by statistical mechanics, which include the occupation probability, the law of equipartition, a detailed balance, and the law of kT/C. In addition, the counting statistics on the directional motion (i.e., the current) of the single-electron thermal noise indicate that the individual electron motion follows the Poisson process, as it does in shot noise.

Bound exciton photoluminescence from ion­implanted phosphorus in thin silicon layers.

We report the observation of clear bound exciton (BE) emission from ion-implanted phosphorus. Shallow implantation and high-temperature annealing successfully introduce active donors into thin silicon layers. The BE emission at a wavelength of 1079 nm shows that a part of the implanted donors are definitely activated and isolated from each other. However, photoluminescence and electron spin resonance studies find a cluster state of the activated donors. The BE emission is suppressed by this cluster state rather than the nonradiative processes caused by ion implantation. Our results provide important information about ion implantation for doping quantum devices with phosphorus quantum bits.

Single-electron transport through single dopants in a dopant-rich environment.

We show that single-electron transport through a single dopant can be achieved even in a random background of many dopants without any precise placement of individual dopants. First, we observe potential maps of a phosphorus-doped channel by low-temperature Kelvin probe force microscopy, and demonstrate potential changes due to single-electron trapping in single dopants. We then show that only one or a small number of dopants dominate the initial stage of source-drain current vs gate voltage characteristics in scaled-down, doped-channel, field-effect transistors.

Metal--semiconductor transition in single-walled carbon nanotubes induced by low-energy electron irradiation.

We report the effect of low-energy (1 keV) electron beam irradiation on gated, three-terminal devices constructed from metallic single-walled carbon nanotubes. Pristine devices, which exhibited negligible gate voltage response at room temperature and metallic single-electron transistor characteristics at low temperatures, when exposed to an electron beam, exhibited ambipolar field effect transistor (room temperature) and single-electron transistor (low temperature) characteristics. This metal-semiconductor transition is attributed to inhomogeneous electric fields arising from charging during electron irradiation.