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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hetero- and homoepitaxial Nd3+-doped LaF3 thin films have been grown by molecular beam epitaxy. Two different orientations of CaF2 substrates, (111) and (110), have been used for the heteroepitaxial structures. High-resolution emission and excitation spectra as well as the decay time of the emission have been measured. The spectroscopic measurements demonstrate that one Nd3+ site is present in the LaF3 layers grown on CaF2(111) substrates but two slightly different Nd3+ centers are resolved in the films on CaF2(110) substrates. One Nd3+ site has been found in the homoepitaxial sample. Slight differences are observed between the centers found in the LaF3 layers and the one observed in the Nd3+-doped LaF3 bulk crystal. For the homoepitaxial layer, the linewidths are similar to those of the bulk crystals, whereas for the heteroepitaxial layers, a broadening is observed. © 1999 American Institute of Physics.
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  • 2
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new electron cyclotron resonance (ECR) ion source (LECR3—Lanzhou Electron Cyclotron Resonance Ion Source No. 3) has been constructed this year. The main purpose of this source is to provide highly charged ion beams for atomic physics and surface physics research. The design of this ion source is based on the IMP 14.5 GHz ECR ion source (LECR2—Lanzhou Electron Cyclotron Resonance Ion Source No. 2) with double rf heating by inserting waveguide directly and aluminum chamber. Furthermore, the volume of the plasma chamber is larger than that of LECR2 so as to increase the rf power and improve beam intensity for highly charged ions. But the hexapole field on the chamber wall is kept the same value in order to compare with the performance of LECR2. After only four days conditioning the first test results were obtained. The final result of this ion source is expected to be better than LECR2's. © 2002 American Institute of Physics.
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new method for investigation of diffusion processes in liquid metals with solid/liquid–liquid/solid trilayer systems is described. The design of this kind of trilayers enables diffusion processes with no effects from gravity-induced convection and Maragoni-convection conditions. The Ta/Zn–Sn/Si trilayers were prepared and the interdiffusion of liquid zinc and tin at 500 °C was investigated. The interdiffusion coefficients range from 1.0×10−4 to 2.8×10−4 mm2/s, which are less than previous values measured by capillary reservoir technique under 1 g environment where various kinds of convection exist. It is the removing of disturbances of these kinds of convection that brings about the precise interdiffusion coefficients in liquid metals. © 1998 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1858-1868 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several ideas of color encoding for surface slope measurements are systematically explored and reviewed to develop a new set of fundamental concepts. It is shown that different systems, such as shadowgraphs, Schlieren optics, and our water surface gradient detectors, can also be universally described through the concepts of sun glitter functions, incident light-source encoding, and observer encoding. These concepts provide a more precise way of mathematically formulating and physically interpreting the flow visualization images, thereby providing quantitative results. It is this new system of concepts that uncover the quantitative potential of these optical methods. The measurement abilities of various existing optical systems are thus enhanced from qualitative observation or visualization to the well-defined quantitative measurement. This is a critical step forward. The concepts can also be further extended to measure fluid flows with multiple density layers or flows with continuous density variations. As an example of implementation, the method of measuring a water-surface gradient is extended into a reflective approach of detecting small changes of surface slope at an air–water interface. In this process, fluid surface slopes (surface gradients) are first optically mapped into color space. An array of lenses is used to transform the rays of an optical light source into a series of colored parallel light beams by passing the light through a group of two-dimensional color palettes at the focal planes of the lens array. This system of parallel light beams is used to illuminate a free surface of water. The reflected rays from the free surface are captured by a charge-coupled device color camera located above the surface. The slopes are derived from the color images after the calibration, and surface elevations are obtained by integrating the slopes. This technique is then applied to observe free-surface deformations caused by near-surface turbulence interacting with the free surface. © 1996 American Institute of Physics.
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The absorption cross section of a number of calcium salts has been assessed at the calcium L edge by measuring the total electron yield (TEY) at the NSLS U13UA beamline. TEY was used because of distortions introduced by instrumentation when using a transmission signal. The effect of these distortions has been evaluated and is presented. The TEY signal was normalized to the incident beam using the signal from a new beam monitor which is detailed here. Comparative spectra are presented for some calcium salts associated with osteoarthritis. © 1995 American Institute of Physics.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several versions of Mevva ion sources have been developed in our institute since 1988. It operates in a pulsed mode with a pulse length of 1.2 ms and a repetition rate of up to 50 pps. A time-averaged beam current of 10 or 50 mA has been extracted at 30–80 kV from Mevva IIA-H and Mevva IIB, respectively. In order to develop surface modification of materials by ion implantation we have constructed three kinds of Mevva ion source implantation systems. High dose (3–5×1017 cm−2) implantation with Ti, Ce, Y, and Ti+C, etc. has been carried out for improving the lifetime of metal cutting tools, relay contacts, dies, and some sophisticated components.
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  • 7
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Soft X-ray Undulator beamline at the NSLS supports a soft x-ray imaging program including scanning transmission microscopy, scanning photoemission microscopy, Gabor and Fourier transform holography, and large angle diffraction. Zone plates from an LBL Center for X-ray Optics/IBM collaboration are used as optical elements. The current instrumentation of the beamline and the experimental stations is discussed, along with plans for the future at the NSLS and prospects for imaging programs at third generation sources.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Synchrotron radiation can furnish Mössbauer radiation sources with higher brightness compared with conventional radioactive γ-ray sources when nuclear resonant Bragg scattering of synchrotron radiation is utilized. So far the observation of nuclear resonant Bragg scattering has been successfully carried out using single crystals containing 57Fe isotope at INP, HASYLAB, and BNL. We intend to use 57Fe/Fe multilayers instead of the crystals as a nuclear scatterer. In order to observe nuclear resonant scattering it is necessary to suppress Thomson electronic scattering which makes a huge background noise. In the case of the multilayer containing 57Fe and 56Fe only, nuclear resonant Bragg scattering can be observed in the absence of electronic Bragg scattering. Computation of the reflected intensities from a multilayer was made by the method analogous to that used in the design of a multilayer interference filter for a visible ray. Multilayers were fabricated by depositing alternate layers of 57Fe and 56Fe with designed layer thicknesses of 8 and 12 A(ring), respectively. As substrates, quartz glass plates and quartz crystal plates were used. The substrates were cooled by liquid nitrogen. The structure of the multilayer was characterized by Mössbauer γ-ray diffraction. The 14.4-keV γ-rays from 57Co source were used. A rocking curve has a peak, when measured under the resonance condition. The Bragg angle of the peak coincide well with that calculated from the designed spacings. From these facts it is concluded that the peak corresponds to nuclear resonant Bragg scattering.
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  • 9
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A simple low-voltage (20-kV) UHV-compatible Mott polarimeter is described that incorporates an in-line retarding potential energy analyzer that, at incident electron energies ≤50 eV, provides an energy resolution of ≤0.5 eV. The polarimeter is very compact and is suitable for use in a wide variety of applications requiring energy- and angle-resolved polarization measurements.
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  • 10
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an experimental and theoretical study of the size dependence of the coupling between electron–hole pairs and longitudinal-optical phonons in Ga1−xInxN/GaN-based quantum wells and quantum boxes. We found that the Huang–Rhys factor S, which determines the distribution of luminescence intensities between the phonon replicas and the zero-phonon peak, increases significantly when the vertical size of the boxes or the thickness of quantum well increases. We assign this variation to (1) the strong electric field present along the growth axis of the system, due to spontaneous and piezoelectric polarizations in these wurtzite materials, and (2) the localization on separate sites of electrons and holes in the plane of the wells or boxes, due to potential fluctuations in the ternary alloy. Indeed, envelope-function calculations for free or localized excitons, with electron–hole distance only controlled by Coulomb interaction, do not account quantitatively for the measured behavior of the S factor. In fact, the latter is rather similar to what is obtained for donor–acceptor pairs, with a statistical distribution of distances between localization centers for electrons and holes. © 2002 American Institute of Physics.
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