So far, most of the experimental results for the core-level spin-resolved photoemission from non-magnetic materials have been interpreted by a simple free-atom model. However, the multiple scattering exerts some influence on the spin polarization. We thus have theoretically investigated the effect of multiple scattering on the spin polarization in W4ƒ photoemission spectra from W(110) surface. The present multiple scattering calculation improves the agreement with the experimental results in comparison with the calculation using the free-atom model. To understand the effect of multiple scattering on spin polarization, we calculated the spin polarization from emitter atoms in the individual surface layers. We found that the forward scattering plays an important role. We also studied the effect of thermal factor on spin polarization, and found that it was quite small.
A scanning near-field optical microscope (SNOM) combined with a scanning tunneling microscope (STM) is used to investigate nanoscopic optical phenomena both in the near-field region and in the proximity. The system is realized by introducing a doubly metal-coated optical fiber tip with an extremely small aperture, on which metal-coating is performed to obtain a half-transparent conducting tip. A simultaneous SNOM/STM observation is performed for an Au (111) surface, where the evanescent field standing on the tip vicinity through the aperture is scattered by the local structures of the sample and the far-field component of the scattered light is collected as an optical signal. The distance con-trol is carried out under constant current condition in order to separate the optical properties from surface topography. λ/100 optical resolution and the identical channel transport both for electrons and photons are achieved.
In this paper, the effects of hydrogen in H-MBE (atomic hydrogen-assisted molecular beam epitaxy) have been investigated. We have found that atomic hydrogen is very useful for substrate cleaning in low temperature, surfactant effects such as restrain of island growth and enhancement of layer-by-layer growth, and selective growth on masked substrates. The main mechanism of the selective growth under atomic H irradiation is Ga and As re-evaporation in the form of hydrides from the mask. In addition, atomic hydrogen plays an important role in the achievement of uniformly formed self-organization-quantum dots (QDs) by passivation of surface-step. On the other hand, it has been observed that the enhanced Al re-evaporation from the GaAs(001) substrate arises via formation of Al hydrides during A1GaAs layer growth.
The shave-off depth profiling is one of the most powerful techniques to obtain accurate elemental depth distributions from small particles and samples with rough surfaces. In order to clarify the factors determining the depth resolution and to estimate the ultimate depth resolution by the shave-off depth profiling, simulations of shave-off process and experiments on a model multilayer sample were performed. The simulation revealed that the key factors to realize the best depth resolution were alignment of the primary beam and the sample, and the shave-off speed. The simulation showed the best depth resolution of 3nm with precise alignment of the primary beam and the sample under the current experimental setup. From the measured depth profile of a TiN thin layer, the depth resolution of 21nm was determined. When the state-of-the-art focused ion beam is used as the primary beam, the practical depth resolution of 1.4nm is expected for the analysis of the sample with 1μm2 cross section.
A new charge neutralization method for monochromatized X-ray photoelectron spectroscopy was proposed. The point of this method is to mount metal walls around the sample. As X-ray photons irradiate the walls, the electrons which neutralize the surface charge of the sample are emitted. With the metal walls of the high secondary electron emissive materials, the peak shift of the Al2p XPS spectrum for sapphire was smaller than 10 eV; furthermore the differential charging of roughed sapphire surfaces was eliminated. This method can be widely used without complicated adjustment, and is more useful and effective than conventional methods.
A new direct structural analysis method, which is based on the vibrational correlation between the nearest neighbor atoms in crystal, is presented. A very simple oscillation has been observed in the three-dimensional data-set of electron thermal diffuse scattering in a low-to-medium energy range from a Si(001) 2×1 surface. The observed oscillation has been attributed to the coherent diffraction among the nearest neighbor atoms, in which the vibrational correlation is very large. We demonstrate that nearest neighbor pairs of Si(001) 2×1 dimer structure are directly reconstructed by using the Patterson analysis of the observed patterns. The present method is a promising new tool for determining surface structures.
The behavior of monolayer holes on GaAs(001) surface during post-growth annealing in molecular beam epitaxy (MBE) is examined in detail by in-situ scanning electron microscopy (SEM). Submicron scale, nearly rectangular, monolayer deep holes are formed after small islands and holes are eliminated. Their growth and shrinkage are found to proceed asymmetrically: For example, they grow only into the right side, and shrink only from the top. The mechanism is discussed in terms of step activity. It was found that in the regrowth after annealing, three dimensional islands are formed preferentially on the step edges.
In order to elucidate the formation process of a self-assembled monolayer (SAM) of alkylthiophene, a dodecylthiophene film on a gold substrate was analyzed by FT-IR spectroscopy. We found that dodecylthiophene successfully formed the SAM on the gold substrate with three stages in the formation process. In the primary stage, dodecylthiophene adsorbs uniformly on the substrate with the parallel orientation until full coverage is achieved. In the following stage, however, the alkyl-chain moiety aligns up to the normal direction against the substrate, and condenses to a close packed form; simultaneously, the thiophene moiety keeps the parallel orientation. In the final stage, the thiophene moiety orients perpendicular direction in accordance with the alkyl-chain. Our findings indicate that the intramolecular tilt and interaction play important roles in the orientation of the moiety and in the cooperative alkyl-chain orientation, respectively.
When the contact size becomes comparable to electron Fermi wavelength, the electron transport through such a small point contact shows various quantum phenomena. Quantization of conductance is a marked example of such quantum effects. In the case of metal contacts, one has to fabricate atom-sized contacts for observing the quantized conductance. However, thanks to recent developments in nanotechnology, it is now possible to investigate experimentally some properties of quantized conductance in various metallic nanocontacts. In this article, I will give a brief survey of previous studies of quantized conductance in metal nanocontacts. Since this field is relatively new, many aspects of quantized conductance still remain to be identified.
Positron-annihilation induced Auger electron spectroscopy (PASS) makes use of low-energy (∼10 eV) positron beams to create core-hole excitations through matter-antimatter annihilation. PAES has a number of advantages over conventional electron-induced Auger electron spectroscopy: 1) enhanced surface selectivity, 2) elimination of the background of secondary electrons, and 3) extremely low beam-damage. A problem of PAES experiments is a low countrate due to the extremely low beam current of positrons. A time of flight (TOF) system with use of an intense pulsed positron beam makes it possible to measure PAES spectra with higher count-rate and higher energy-resolution than previous apparatus. In the present paper, we describe the mechanism and characteristics of PAES, and then show the details of the TOF-PAES apparatus and applications with it.