Bibliothek

Notizen: This study analyzes synchrotron radiation heat loading effects on optical components of beamline BL12.0 for EUV interferometry and soft x-ray microscopy at the Advanced Light Source (ALS). Newly developed indirect side-cooled beamline optics were considered, and the resulting surface distortion of mirrors and grating indicates that there is no significant degradation of beamline performance in spectral resolution or throughput. Also analyzed are the effects of heat loading on end-station components, such as Fresnel zone plates, transmission gratings, masks and membranes. Experimental results of heat loaded membranes are presented as well in this writing. © 1996 American Institute of Physics.

Notizen: We measured the Schottky barrier heights and specific contact resistivities of four different metals on p-type GaN. The Schottky barrier heights of Pt, Ni, Au, and Ti were obtained from the current-voltage characteristics to be 0.50, 0.50, 0.57, and 0.65 eV, respectively. The specific contact resistivities were 0.013, 0.015, 0.026, and 0.035 Ω⋅cm2, respectively. Our experimental results proved that the Schottky barrier heights and specific contact resistivities decrease with increase in metal work function as expected theoretically. © 1996 American Institute of Physics.

Notizen: This bending magnet beamline has been in operation since February 1995 for the characterization of optical elements (mirrors, gratings, multilayers, detectors, etc.) in the energy range 50–1000 eV. Although it was designed primarily for precision reflectometry of multilayer reflecting optics for EUV projection lithography, it has capabilities for a wide range of measurements. The optics consist of a monochromator, a reflectometer, and refocusing mirrors to provide a small spot on the sample. The monochromator is a very compact, entrance-slitless, varied-line-spacing plane-grating design in which the mechanically ruled grating operates in the converging light from a spherical mirror working at high demagnification. Aberrations of the mirror are corrected by the line spacing variation, so that the spectral resolving power λ/Δλ is limited by the ALS source size to about 7000. Wavelength is scanned by simple rotation of the grating with a fixed exit slit. The reflectometer has the capability of positioning the sample to within 10 μm and setting its angular position to 0.002°. LABVIEWTM based software provides a convenient interface to the user. The reflectometer is separated from the beamline by a differential pump and can be pumped down in 1/2 hour. Auxiliary experimental stations can be mounted behind the reflectometer. Results are shown that demonstrate the performance and operational convenience of the beamline © 1996 American Institute of Physics.

Notizen: Since stratospheric particles have a possibility to make a large effect on the climate in a global scale, a number of observations have been carried out using different techniques.1 Those particles were found to consist of mainly sulfuric acid and to be 0.1–1.0 μm in size. Turco and co-workers proposed a model that the particles are formed through chemical and physical processes initiated by photodissociation of OCS (λ〈2600 A).2 In order to examine this model, a simulation experiment in a laboratory system has been planned, in which ultraviolet components of SR are utilized. An optical system including a Seya-Namioka monochromator has been designed, constructed, and tuned precisely.3 In this system, the first prefocusing mirror (sphere) deflects the SR beam horizontally by 30°, and the second and the third ones (sphere) focus the beam vertically onto the entrance slit of the monochromator. The grating radius is 0.5 m. The monochromatized photon beam is reflected into the horizontal direction by the postfocusing mirror (toroid). A ray-tracing calculation was performed, and the obtained spot diagrams showed that the widths of the rays are about 100 μm at the two slits, and the spot size is 1.5×0.8 mm2 at the experimental point.These calculated results were confirmed experimentally by using visible and ultraviolet components of SR. From an estimation on the rate of the particle formation using the data available in the literature, the rate determining step was found to be the photodissociation of OCS in the ultraviolet region. At first, the photoabsorption spectra (cross section) were measured at room temperature and at −80 °C (near to the stratospheric temperature). The spectrum is composed of a broad band centered at 2250 A(ring) and of a number of small peaks. Photodissociation rates of OCS at several altitudes have been calculated using the present cross-section values, which indicated that the life of OCS is about 15 years at 20 km and two months at 30 km. It is known that CO and S are formed through the photodissociation of OCS. A computer-controlled mass spectrometer was made for pursuit of the time variation of CO density in the reaction cell, in which the sample gas, a few percent OCS in He, is introduced and irradiated by the photon beam. A chamber has been designed and constructed, in which a pseudostratospheric air is being irradiated by the ultraviolet radiation. A particle counter of laser-scattering type is being connected to this chamber in order to observe the particle number in it. The present study is the first examination applying SR to problems in the stratosphere as a simulated solar radiation. The obtained results have shown opening a new scientific opportunity in the utilization of SR.

Notizen: An electrodeless method has been applied to the measurement of an ionic conductivity of a single crystalline RbAg4I5 as a function of temperature. The activation energy obtained by this method is in good agreement with those of earlier works.

Notizen: Temperature dependences of the hole concentration and Hall mobility in Mg-doped GaN and Al0.08Ga0.92N grown by metalorganic vapor phase epitaxy were measured by the van der Pauw method over a wide temperature range from 100 to 500 K. Assuming that the effective mass of holes in Al0.08Ga0.92N is equal to that of GaN, the activation energy of the Mg shallow acceptor in Al0.08Ga0.92N is estimated to be about 35 meV deeper than that in GaN.

Notizen: p-type conduction in InN-containing nitrides doped with Mg has been achieved by metalorganic vapor-phase epitaxy. The hole concentration at room temperature is as high as 7×1017 cm−3. The activation energy of a Mg acceptor is estimated to be 204 meV. D–A pair emission with peak wavelength of about 405 nm is enhanced by thermal annealing. © 1995 American Institute of Physics.

Notizen: High-quality Ga0.92In0.08N–GaN multiple quantum wells structures (MQW) were grown successfully by metalorganic vapor phase epitaxy. Fine multilayer structures with a thickness period of 7–9 nm were detected by secondary ion mass spectroscopy. The dislocation density in the MQW was found to be in the range of 0.5–2×109 cm−2 by transmission electron microscopy. The MQW extremely enhanced by two orders of magnitude, the cathodoluminescence intensity compared with bulk Ga0.91In0.09N. © 1996 American Institute of Physics.

Notizen: Intermediate states near the normal–superconducting transition at ∼100 mK, important for a sensitive thermometer in x-ray calorimetry, have been studied by an imaging technique based on low temperature scanning synchrotron microscopy (LTSSM). In conjunction with iridium superconducting transition-edge sensors (TES) operating in electrothermal feedback mode, the LTSSM visualizations reveal that a normal–superconducting phase separation actually takes place in the intermediate states. © 2002 American Institute of Physics.

Notizen: Imaging diagnosis of superconducting tunnel junction x-ray detectors has been performed by an apparatus called the low-temperature scanning synchrotron microscope (LTSSM) using an x-ray microbeam with a diameter of 5–10 μm originated from synchrotron radiation. Quasiparallel intense synchrotron radiation enables one to obtain the full two-dimensional images of junctions with dimensions of 200×200 μm2 in about 1 h. The LTSSM results indicate that the standard quasiparticle diffusion and edge loss model for the spatial distribution of the junction response to x rays is evidently inadequate for intermediate or large junctions (with respect to a Josephson penetration depth). On this basis, it is argued that the models proposed for the signal creation and loss mechanism should be reconsidered. © 2000 American Institute of Physics.