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91.
Ph. Boullay G. TrolliardD. Mercurio J.M. Perez-MatoL. Elcoro 《Journal of solid state chemistry》2002,164(2):252-260
A generalized structural model of Aurivillius-type compounds is presented using a 4D superspace group analysis where Aurivillius structures are considered as cation-deficient perovskites with the general formula AB1−xO3. Being essentially composition independent, the model is valid for any Aurivillius-type compounds where x is the only composition-dependent parameter. The atomic domains representing the atoms in superspace are described by means of crenel functions. For any composition, the conventional space groups can be easily derived from a unique superspace group. This work is supported by a TEM investigation where the continuously variable character of the diffraction diagram indicates that the various stacking sequences can be interpreted in terms of a structural modulation over a common average structure. 相似文献
92.
Sebban S Mocek T Ros D Upcraft L Balcou P Haroutunian R Grillon G Rus B Klisnick A Carillon A Jamelot G Valentin C Rousse A Rousseau JP Notebaert L Pittman M Hulin D 《Physical review letters》2002,89(25):253901
We report the first experimental demonstration of a Ni-like optical-field ionization collisional soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 760 mJ, 30 fs, 10-Hz Ti:sapphire laser beam in a few mm cell filled with krypton. We have measured a gain coefficient of 78 cm(-1) on the 3d(9)4d 1S0-3d(9)4p(1)P1 transition at 32.8 nm, which is here amplified for the first time. This radiation source represents the shortest wavelength optical-field ionization collisional soft x-ray laser ever produced. The influence of the gas pressure and the pumping energy on the lasing output are also presented. 相似文献
93.
A strong electric susceptibility is measured as a function of temperature in a molecular dimer which is weakly bound by a pair of hydrogen bonds. This system is a remarkable example where the dominant term in the susceptibility is due to a vibration induced electric dipole. As a consequence, the averaged square of the dipole moment varies linearly with the temperature and the susceptibility does not follow the usual 1/T Curie law. this spectacular effect demonstrates the importance of dynamics to interpret the properties of weakly bound complexes. 相似文献
94.
Single element quasicrystalline monolayers were prepared by deposition of antimony and bismuth on the fivefold surface of icosahedral Al71.5Pd21Mn8.5 and the tenfold surface of decagonal Al71.8Ni14.8Co13.4. Elastic helium atom scattering and low energy electron diffraction of the monolayers show Bragg peaks at the bulk derived positions of the clean surfaces, revealing highly ordered quasicrystalline epitaxial films. Their adatom densities of (0.9+/-0.2)x10(15) cm(-2) and (0.8+/-0.2)x10(15) cm(-2) on Al-Pd-Mn and Al-Ni-Co, respectively, correspond to roughly one adatom per Al atom of the quasicrystalline substrate surfaces. 相似文献
95.
Bréchignac C Cahuzac P Concina B Leygnier J Ruiz LF Zarour B Hervieux PA Hanssen J Politis MF Martín F 《Physical review letters》2002,89(18):183402
We present a combined theoretical and experimental study of charge transfer and dissociation in collisions of slow Li31(2+) clusters with Cs atoms. We provide a direct quantitative comparison between theory and experiment and show that good agreement is found only when the exact experimental time of flight and initial cluster temperature are taken into account in the theoretical modeling. We demonstrate the validity of the simple physical image that consists in explaining evaporation as resulting from a collisional energy deposit due to cluster electronic excitation during charge transfer. 相似文献
96.
Heinze S Tersoff J Martel R Derycke V Appenzeller J Avouris P 《Physical review letters》2002,89(10):106801
We show that carbon nanotube transistors operate as unconventional "Schottky barrier transistors," in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance. Transistor characteristics are calculated for both idealized and realistic geometries, and scaling behavior is demonstrated. Our results explain a variety of experimental observations, including the quite different effects of doping and adsorbed gases. The electrode geometry is shown to be crucial for good device performance. 相似文献
97.
Bréchignac C Cahuzac P Carlier F Colliex C Leroux J Masson A Yoon B Landman U 《Physical review letters》2002,88(19):196103
Formation and evolution of fragmentation instabilities in fractal islands, obtained by deposition of silver clusters on graphite, are studied. The fragmentation dynamics and subsequent relaxation to the equilibrium shapes are controlled by the deposition conditions and cluster composition. Sharing common features with other materials' breakup phenomena, the fragmentation instability is governed by the length-to-width ratio of the fractal arms. 相似文献
98.
Deninger AJ Eberle B Ebert M Grossmann T Heil W Kauczor H Lauer L Markstaller K Otten E Schmiedeskamp J Schreiber W Surkau R Thelen M Weiler N 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,141(2):207-216
We present a new method to determine in vivo the temporal evolution of intrapulmonary oxygen concentrations by functional lung imaging with hyperpolarized (3)Helium ((3)He-->). Single-breath, single-bolus visualization of (3)He--> administered to the airspaces is used to analyze nuclear spin relaxation caused by the local oxygen partial pressure p(O(2))(t). We model the dynamics of hyperpolarization in the lung by rate equations. Based hereupon, a double acquisition technique is presented to separate depolarization by RF pulses and oxygen induced relaxation. It permits the determination of p(O(2)) with a high accuracy of up to 3% with simultaneous flip angle calibration using no additional input parameters. The time course of p(O(2)) during short periods of breathholding is found to be linear in a pig as well as in a human volunteer. We also measured the wall relaxation time in the lung and deduced a lower limit of 4.3 min. 相似文献
99.
Oxygen K-edge x-ray absorption spectra were studied on the electrochromic amorphous thin film a-WO3 in the comparison with crystalline oxides having variable electronic (d0, d1, d2) and atomic structure: monoclinic m-WO3 (insulator - d0), cubic Na0.6WO3 (metal - d1), cubic ReO3 (metal - d1), layered-type hexagonal h-WO3, WO3H2O and with intercalated HxReO3 (metal - d2), HxWO3 oxides having a metal-isulating transition. The changes in the XANES range 10–15 eV above the absorption edge are interpreted
based on the known band-structure calculations. The high-energy features are related to the multiple-scattering processes
(EXAFS) on the nearest atoms. The intensity of the feature at 550–560 eV is attributed for the first time to the value of
the metal-oxygen-metal bond angle.
Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998. 相似文献
100.
L. Monz R. Hohmann H.-J. Kluge S. Kunze J. Lantzsch E.W. Otten G. Passler P. Senne J. Stenner K. Stratmann K. Swendt K. Zimmer G. Herrmann N. Trautmann K. Walter 《Spectrochimica Acta Part B: Atomic Spectroscopy》1993,48(14):1655-1671
Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 108 atoms in the presence of about 1018 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 106. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 1010 and an overall efficiency of ξ = 5 × 10−6 have been achieved. The desired detection limit of 108 atoms 90Sr has been demonstrated with synthetic samples. 相似文献