An analytical approach in calculating electron field emission current from a silicon subsurface layer is presented. By employing a nontriangular quantum well model for the silicon subsurface layer, wave functions of e...
A relationship between hexagonal phases in the Zn-Mg-RE (RE=rare earth) system and icosahedral quasicrystalline phase is discussed. There are three hexagonal phases in the vicinity of Zn6Mg3RE1 which are related with ...
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A relationship between hexagonal phases in the Zn-Mg-RE (RE=rare earth) system and icosahedral quasicrystalline phase is discussed. There are three hexagonal phases in the vicinity of Zn6Mg3RE1 which are related with a lattice parameters by a ratio 3:5:7 but with approximately the same c parameters. A structural model for the phase with medium a lattice parameter is proposed based on the structures of the other two phases recently determined. We also show a preliminary result of X-ray diffraction study of the Zn-Mg-Ho icosahedral phase.
We found two types of commensurate-incommensurate transition on Pb-adsorbed Si(111) surfaces using reflection high-energy electron diffraction (RHEED) below room temperature (RT); a hexagonal incommensurate (HIC) phas...
We found two types of commensurate-incommensurate transition on Pb-adsorbed Si(111) surfaces using reflection high-energy electron diffraction (RHEED) below room temperature (RT); a hexagonal incommensurate (HIC) phase changed to a 7×3−Pb superstructure around 250 K, and a transient phase between the HIC phase and a striped incommensurate phase changed to a 43×3−Pb superstructure at 130 K. We constructed a surface structure map in ranges of temperature from 90 K to 500 K and Pb coverage from 0.8 to 1.5 atomic layers including these new phases. We found another structure change where streaks with a 3×3 periodicity began to appear in RHEED just below RT when the 3×3−Pb phase at 1/3 atomic layer of Pb was cooled.
Electron standing waves have been observed near step edges and out-of-phase domain boundaries on the Si(111)-3×3-Ag surface using scanning tunneling microscopy at 6 K. This means that this surface has a two-dimen...
Electron standing waves have been observed near step edges and out-of-phase domain boundaries on the Si(111)-3×3-Ag surface using scanning tunneling microscopy at 6 K. This means that this surface has a two-dimensional free-electron-like surface electronic state. Their wavelengths change with the bias voltages, so that the dispersion relations between energy and wave number have been obtained. We have found two types of out-of-phase domain boundaries of the 3×3-Ag structure, one of which acts as a potential barrier for the surface-state electrons to make the standing waves, while the other type does not.
Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spect...
Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spectroscopically in the visible spectral range. The light emission is based on a novel mechanism involving optical transitions between a tip state and localized states on the sample surface. The wavelength of the photons can be changed by the bias voltage of the STM. The spatial resolution of the photon maps is as good as that of STM topographic images and the photons are emitted from a quasipoint source with a spatial extension similar to the size of a dangling bond.
Excess Ag adatoms of submonolayer coverages on top of the Si(111)-3×3-Ag surface at room temperature (RT) are known to stay in a two-dimensional adatom-gas (2DAG) phase as a thermodynamical equilibrium state. Red...
Excess Ag adatoms of submonolayer coverages on top of the Si(111)-3×3-Ag surface at room temperature (RT) are known to stay in a two-dimensional adatom-gas (2DAG) phase as a thermodynamical equilibrium state. Reducing the diffusion mobility of the Ag adatoms by cooling the substrate down to 62 K, we could observe migrating adatoms in the 2DAG phase directly by scanning tunneling microscopy (STM). The individual Ag adatoms ceased migration completely at 6 K, showing starlike patterns in STM images. The estimated amount of those Ag adatoms frozen at 6 K was on the order of 0.01 ML, which is in accordance with that at RT obtained previously from electrical conductance measurements.
A dense commensurate 3×3 phase was obtained by additional 0.7 ML Pb adsorption onto the Si(111)−3×3−Pb surface (13 ML Pb) at room temperature (RT). Its electronic structure was similar to that of the hexagon...
A dense commensurate 3×3 phase was obtained by additional 0.7 ML Pb adsorption onto the Si(111)−3×3−Pb surface (13 ML Pb) at room temperature (RT). Its electronic structure was similar to that of the hexagonal and striped incommensurate (HIC and SIC) phases. A high surface electrical conductance observed for this phase was attributed partly to an increase of carrier concentration in the surface space-charge layer, and more importantly to the formation of a metallic surface state. The HIC phase, on the other hand, was found to convert to the SIC phase with only 0.08 ML additional Pb adsorption at RT, which was accompanied with a steep increase in conductance. This was due to an increase of carrier concentration in the metallic surface state, and also possibly due to an enhancement of its carrier mobility. Both enhancements are suggested to come from the reduced domain-wall density in the SIC phase compared with the HIC phase.
Surface-enhanced Raman scattering spectroscopy has been applied so that hydrogen chemisorption on the diamond (111) and (100) surfaces could be observed. Raman scattering signals from the surface species were enhanced...
Surface-enhanced Raman scattering spectroscopy has been applied so that hydrogen chemisorption on the diamond (111) and (100) surfaces could be observed. Raman scattering signals from the surface species were enhanced by means of contact with thin Ag films. C−H stretching vibrations were observed in the region 2800–3000 cm−1 from the hydrogenated diamond surface. C-D stretching vibrations were observed in the region 2050–2250 cm−1 from the deuterated diamond surface. C−H and C-D stretching vibration modes were assigned according to ab initio molecular orbital calculations.
Physical mechanisms which limit the squeezing bandwidth in a heterojunction light-emitting diode (LED) have been extensively studied both theoretically and experimentally. It is proven that our experimental results of...
Physical mechanisms which limit the squeezing bandwidth in a heterojunction light-emitting diode (LED) have been extensively studied both theoretically and experimentally. It is proven that our experimental results of pump-current dependence of the squeezing bandwidth in the constant-current-driven heterojunction LED at room temperature cannot be explained by previous theoretical predictions. We present a theoretical framework, including the effects of a microscopic backward-pump (BP) process, generally applicable to a heterojunction LED. Parameters describing the relative significance of the BP process are determined by the measurements of current-versus-voltage characteristic and differential resistance of the LED, independent of the noise measurements. As a consequence, the experimental results can be explained by our model in a unified manner over a whole range of injection current, and it is clarified that the pump situation of the LED moves continuously from thermionic emission to diffusion limits with increasing pump current.
The ground state of a rotating Bose-Einstein condensate with attractive interaction in a quasi-one-dimensional torus is studied in terms of the ratio γ of the mean-field interaction energy per particle to the single-...
The ground state of a rotating Bose-Einstein condensate with attractive interaction in a quasi-one-dimensional torus is studied in terms of the ratio γ of the mean-field interaction energy per particle to the single-particle energy-level spacing. The plateaus of quantized circulation are found to appear if and only if γ<1 with the lengths of the plateaus reduced due to hybridization of the condensate over different angular-momentum states.
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