Microscopically controlled oxidation of H/Si(1 0 0) by lateral surface electric field studied by emission electron microscopies

The ultrathin oxidation of a H/Si(1 0 0) surface with microfabricated pn-junctions was studied by photoemission electron microscopy (PEEM), mirror electron microscopy (MEM) and microscopic X-ray photoelectron spectroscopy (μ-XPS). The ultrathin oxidation inverts the contrast of the junctions in PEEM images. It is found by analyzing the intensity profiles of images that the potential distribution across the pn-junctions is also inverted by the oxidation. The charging of the oxide by ultraviolet irradiation from a light source of PEEM is attributed as the cause of the inversion of the contrast shown by μ-XPS and MEM.     

Bose-Einstein correlations for pions produced inp p collisions at 360 GeV/c

Zeitschrift für Physik C Particles and Fields - Correlations among identically charged pions were measured for pions produced inp p collisions at 360 GeV/c using the EHS spectrometer. The...     

Frequency metrology with a turnkey all-fiber system

The repetition rate and carrier-envelope phase offset frequencies of a turnkey, all-fiber-based continuum generator were phase locked to a hydrogen maser. The frequency of the hydrogen maser was calibrated with a highly stable cesium atomic clock, and therefore a fully phase-locked optical frequency comb with well-defined absolute frequencies was obtained. In contrast with the commonly used Ti:sapphire-laser-based systems, we have accomplished a fully turnkey system with no user-adjustable parts. To evaluate the performance of this novel system, we performed absolute frequency measurements in the telecommunications region and at 1064 nm and compared them with our traditional Ti:sapphire-based comb.     

Nuclear Spin–Lattice Relaxation of Single Crystal Sr14Cu24O41

Nuclear spin–lattice relaxation rate T ₁ ⁻¹ has been measured for the ladder sites of two single crystals Sr₁₄Cu₂₄O₄₁ (Sr14-A,B) by ⁶³Cu NMR/NQR. The hole localization around 100 K appears as a peak in the T variation of T ₁ ⁻¹(NQR). On the other hand, it is suppressed in the T ₁ ⁻¹ (NMR) data under the magnetic field H ∼ 11 T, and a new peak appears around 20 K. T ₁ ⁻¹(NMR) around the peak is more enlarged for Sr14-B than for Sr14-A. Hence, holes on the ladders of Sr14-B tend to be more localized. This is considered to be an origin for the occurrence of the magnetic order in Sr14-B under H ∼ 11 T.     

Multi-moment advection scheme for Vlasov simulations

We present a new numerical scheme for solving the advection equation and its application to Vlasov simulations. The scheme treats not only point values of a profile but also its zeroth to second order piecewise moments as dependent variables, for better conservation of the information entropy. We have developed one-and two-dimensional schemes and show that they provide quite accurate solutions within reasonable usage of computational resources compared to other existing schemes. The two-dimensional scheme can accurately solve the solid body rotation problem of a gaussian profile for more than hundred rotation periods with little numerical diffusion. This is crucially important for Vlasov simulations of magnetized plasmas. Applications of the one- and two-dimensional schemes to electrostatic and electromagnetic Vlasov simulations are presented with some benchmark tests.     

Discrete dihedral-angle modulation in porphyrin wheels adsorbed on Cu(1 0 0) observed by scanning tunneling microscopy

Conformations of two dodecameric porphyrin wheels adsorbed on a Cu(1 0 0) were probed by using scanning tunneling microscopy (STM). Whereas a wheel consisting of six meso-meso linked diporphyrins was detected as uniform ring structure, several different images with three discrete molecular heights were detected for a wheel consisting of six meso-meso, β-β,β-β triply-linked planar diporphyrins. These results indicate that the former has a conformation similar to that in a free space, while the latter has various conformations with respect to orientation of planar diporphyrin units toward the metal surface. Several discrete STM images of the latter have been interpreted in terms of possible eight conformations, which vary as to relative orientation of neighboring diporphyrin units.     

Thermal and photochemical reactivity of oxygen atoms on gold nanocluster surfaces

Reduction of oxidized gold nanoclusters by exposures to foreign gases and irradiation of UV photons has been investigated using X-ray photoelectron spectroscopy. Gold nanoclusters with narrow size distributions protected by alkanethiolate ligands were deposited on a TiO₂(1 1 0) surface with dip coating. Oxygen plasma etching was used for removal of alkanethiolate ligands and oxidization of gold clusters. The oxidized gold clusters were exposed to CO, C₂H₂, C₂H₄, H₂, and hydrogen atoms. Although, C₂H₄ and H₂ did not show any indications of reduction of oxidized gold clusters, CO, C₂H₂, and hydrogen atoms reduced the oxides on gold cluster surfaces. Among them, hydrogen atoms were most effective for reduction. Irradiation of UV photons around 400 nm could also reduce the oxidized gold clusters. The photochemical reduction mechanism was proposed as follows. The photo-reduction was initiated by electronic excitation of gold clusters and oxygen atoms activated reacted with carbon atoms at the surfaces of gold clusters. Carbon species were likely absorbed in gold clusters or remained at the boundaries between gold clusters when gold clusters agglomerated during oxygen plasma exposures. As the photochemical reduction progressed, carbon atoms segregated to the surfaces of gold clusters.     

Noise reduction combining time-domain epsilon-filter and time-frequency epsilon-filter

A time-domain epsilon-filter (TD epsilon-filter) is a nonlinear filter that can reduce noise while preserving a signal that varies drastically, such as a speech signal. Although the filter design is simple, it can effectively reduce noise. It is applicable not only to stationary noise but also to nonstationary noise. It cannot, however, be applied when the amplitude of noise is relatively large. This paper introduces an advanced method for noise reduction that applies an epsilon-filter to complex spectra, namely a time-frequency epsilon-filter (TF epsilon-filter). This paper also introduces noise reduction combining a TD epsilon-filter and a TF epsilon-filter. An advanced method called a variable time-frequency epsilon-filter is also proposed. First, the algorithm of the TD epsilon-filter is explained to clarify the problem. Then, the algorithms of the proposed methods are explained. By utilizing an epsilon-filter in the frequency domain, the proposed method can reduce not only noise that has a relatively small amplitude but also noise that has a relatively large amplitude. Experimental results are also given to demonstrate the performance of the proposed methods in comparison to the results of some conventional methods.     

High-throughput characterization of local conductivity of Nd0.9Ca0.1Ba2Cu3O7−δ thin film by the low-temperature scanning microwave microscope

We developed a scanning microwave microscope (SμM) designed for high-throughput electric-property screening as well as for rapid construction of electronic phase diagrams at low temperatures. As a sensor probe, we used a high-Qλ/4 coaxial cavity resonator to which a thin needle with ball-tip end was attached. The sensor module was mounted on the low-temperature XYZ stage, which allowed us to map out the change of resonance frequency and quality factor due to the local tip-sample interaction at low temperatures. From the measurements of combinatorial thin films, such as Ti_1−xCo_xO_2−δ and Nd_0.9Ca_0.1Ba₂Cu₃O_7−δ (NCBCO), it was demonstrated that this SμM system has enough performance for the high-throughput characterization of sample conductance under variable temperature conditions.